Help understanding why my Nibe charge pump is suddenly behaving oddly

samirrpatel · 17 May 2025 12:43

Hi everyone! I’m a newly signed up member but have been browsing the forums here for a little while now trying to make sense of my heat pump data and learning how I can make sure it’s running efficiently. I can see there a lot of helpful and knowledgeable forum members so I am hoping someone can point me in the right direction.

Recently we moved over to the eon next drive tariff which has a daily off-peak period between 0000 - 0700. To take advantage of the cheaper electricity between those hours I wanted to set my Nibe F2040 / SMO 20 system up so that it attempts to heat water only during (i) the off-peak period and (ii) between 1530-1630 to ensure water is available for the evening. On weekdays typically showers are taken between 0615-0645 and then occasionally evening showers anytime from 1700-1900 (hence the 1 hour heating window in the afternoon, assuming ~15min of off-peak heating from the morning would not be sufficient to have the 300L tank up to a reasonable temp).

I have data feeding into Home Assistant via the myUplink integration and would like to work out how to integrate it with OEM eventually. Unfortunately whilst I can see lots of data I’m not really sure what a lot of it means and am somewhat shooting in the dark when trying to diagnose recent issues.

Initially, my installer (who is unfortunately not very responsive at the best of times) had created a schedule which set the DHW to “economy” during the times I wanted the system to heat the water. That was seemingly working ok but then I believe I accidentally made some changes to some settings via the home assistant app (accidental settings change on sliders. Those changes caused our system to start behaving oddly but with the help of the HA history view I think I was able to look back and revert the settings and the system returned to its prior pattern. However in this state I noticed the “add heat in tank” binary sensor (which I believe to be the immersion heater) was kicking in during times outside what had been scheduled. I flagged this to the installer but they said they had trouble seeing my data in myUplink and they asked me to contact Nibe. Upon doing so, Nibe suggested I instead schedule the system to be “off” during periods when I don’t want the water to be heated. I change this on the evening of Wednesday 14th May. Initially this seemed to be working (for around ~12-15 hours) but then on the evening of Thursday 15th May at around 10pm the charge pump turned on and remained on for ~20+ hours. I noticed that the DM value dropped from 0 to -489 when the charge pump initially switched on and I don’t really understand what drove that. I tried to reset the DM manually in HA to zero but it immediately dropped back down to -450 which I believe is the reason the charge pump is continuously running. Even though the charge pump was constantly on, water in the tank was not being heated and at around 6pm on Friday 16th May there was a cold shower had and I was not popular!

Worrying that the continuously on charge pump was running up my electricity bill but more importantly might have been damaging the equipment, I reverted to the original “economy when I want it” schedule that the installer has setup. Things again looked ok for a while and we had hot water this morning (May 17th). There was a bi-weekly legionnaire’s cycle overnight which took the temp to 60C but I understand that’s normal so I thought we were back to good state. The charge pump wasn’t continuously on…but then around 8am this morning (May 17th) I saw the charge pump is back on and the DM reading is negative again. I’ve attached a screenshot (I highlighted in blue the times when the schedule was changed. The red highlight is the time of the cold shower. I’m not really sure the screenshot in itself is that useful and I’d be happy to zoom in / show different metrics if anyone with a bit more experience of these systems can provide me with some guidance as to what is most relevant but I figured I’d share some data in case someone can see anything obvious. One thing I do see is the “flow line temp at 30C” is set to 63C which looks odd (but I don’t know if that setting was recently changed somehow). It seems inconsistent as the settings for 10C/20C are much lower at 26C/15C respectively and presumably the setting at 30C should therefore be lower. Maybe around 10C?

Any help would be very much appreciated and hopefully in time I can learn how this all works and give back to the community too!

Adding a second screenshot which might be helpful. Shows pump speed / DM / hot water top and charging.

dMb · 18 May 2025 09:06

Hi Samir,

Welcome to the forums and thanks for such a clear and comprehensive introductory post. We have a small but growing community of people on here with NIBE systems who have a good understanding of how they work and what the (many!) data parameters relate to. The Home Assistant integration with myUplink is good but it does just dump all the parameters into HA, which tends to be unhelpful until you learn which ones to focus on.

The first thing I’ll highlight is that the DM (Degree Minutes) value is purely related to Central Heating and is completely separate from the DHW management. (If you’re not familiar with the principle of DMs, they’re a way for the controller to keep track of under- or over-shooting the calculated target flow temperature for space heating.) It’s a read-only parameter, so not something you can set directly - though you can adjust the DM threshold values for things like compressor start-up.

The second thing I’ll highlight is not to worry about the charge pump running most of the time. Mine runs 24x7 during the heating season, and only consumes about 10W. It needs to run at a low level to move water through the central heating system - especially on installations with a buffer tank / volumiser vessel - then it ramps up to 100% when it needs to.

A few other initial thoughts:

I’d recommend changing settings via the SMO 20 controller rather than via Home Assistant - at least until you are confident things are behaving themselves
- Firstly because that’s what most NIBE owners on the forums (and NIBE themselves) will be familiar with
- Secondly because the SMO 20 will enforce a level of consistency between different parameters that I’m not sure the Home Assistant integration knows how to do
In terms of your original objective of aligning DHW runs with the off-peak tariff, the advice from NIBE was correct - you’ll want to tell the system not to heat the hot water at all during the daytime
- The SMO 20 uses the terminology of scheduling ‘Blocking’ of DHW during the times you don’t want it to run
There are relatively few settings which influence DHW heating - basically just the schedule and the ‘Economy’ versus ‘Luxury’ setting (which controls the target DHW tank temperature) - whereas most of the complexity is around space heating
- Are you needing much space heating at the moment? It might be simpler to remove that from the equation (for now) by setting a low room temperature, so that your graphs only reflect what’s happening for DHW

David

samirrpatel · 18 May 2025 14:30

Hi David,

Thanks for taking the time to respond. My wife is thinking of “banning me from tinkering” so I’m pleased I can say I’ve received some expert opinion. My ultimate aim is to understand this system well enough during the summer months so that by the time the winter arrives I’ve got some idea of how to run things most efficiently, so I’ve told her some experimentation is going to be necessary!

Point noted on the “blocking schedule”. I’ll try that again, though I might be in the doghouse if there’s another cold shower! Oddly, the “non-blocking” schedule seems to have no effect then. E.g. at present I have it set to economy between 0000-0700 and 1530-1630 but today we had showers starting at approximately 1340 after a morning of sports/gym and the water heating appears to have kicked in at around 1350 (I’m basing this statement on the charge pump being “on” and the “BT6 - Hot water charging” reading steadily increasing). As I write the charge pump remains on and it’s only ~1445 so the heating took place entirely outside of the scheduled time. Maybe my ASHP doesn’t have the clock set correctly? I’ll check that and report back.

Aha! So I’ll stop looking at DM for my DHW question, though that does mean I have another mystery to solve. I have no idea how the DM suddenly dropped from ~0 to ~-490 almost instantly on Friday evening (at least I thought I had seen that but now looking in HA the reported history says otherwise, albeit I do see the DM was very negative for most of Friday. I’m based on London and it wasn’t particularly cold so I don’t think that should be happening. As for where the myUplink integration can reset that value…I did think I managed to set it to zero at some point yesterday (see red circle on the screenshot). After doing so the integration seems to crash and then I had to restart it so maybe it’s not supposed to be editable in the first place. Perhaps it’s best that I initially just make everything read-only in the integration to avoid any accidental fat fingers causing unintended consequences. I’ll see if I can do that from the myUplink website. I have a vague recollection of selection Read/Write when setting up the API Key. Anyway, after setting the DM to zero yesterday it again starting moving slowly negative. I also

On the charge pump being on for long periods I confirmed it was running at 30% for most of the time (which I think is the minimum). I’ll try and work out how much electricity that used (I know our usage was much higher than usual yesterday and I’m not sure why). I don’t currently have a way to accurately measure the electricity usage of the heating system. I am thinking of getting a CT clamp to put around the live wire for the ASHP in my fusebox but I think that will only tell me how much electricity the heatpump in the back garden consumes (i.e. I’m not sure if it’ll include the charge pump).

Noted. Hopefully I can set it up appropriately and then leave it to its own devices, although the tinkerer in me was thinking about having HA automations that would outsmart what NIBE have coded up in the SMO 20 (e.g. making it “Luxury” during the off-peak period to get the water extra hot but then dropping it back down to “Economy” for any further heating that happens in the afternoon peak period. Perhaps I’ll put that idea on ice given recent experience!

We’ve got UFH throughout and I’m fairly certain nothing has been on these past few days. Is there a way to change a setting which will ensure that is removed from the equation for now? One think I did think was odd and I did change was the “flow line temp at 30C”. I don’t really understand what the 7 different (-30/-20/-10/0/10/20/30) flow line settings do but the value for the 30C one looked odd so I did set it to 10C yesterday (to be below the 15C for the flow line at 20C value). Could the previous value of 63C been what was making the DM so negative (I’m somewhat skeptical of that theory as I don’t see the value having been changed recently so it could have been at 63C for quite a while and perhaps been ignored as the outdoor temp hasn’t got anywhere near 30C?

Lastly, on the subject of getting data into emonCMS (which I am hoping makes it easier for folks on this forum to help me?) I was trying to follow this youtube video which suggests I need to have readings for the below listed metrics (these are the youtuber’s names for his sensors). I’m not sure if my SMO 20 has some of these (I know the power/energy ones will need that CT clamp) but I’m not sure I have DHW on/off binary sensor and I am not sure which of the values I see from myUplink correspond to some of the others (e.g. setpoint). Is there a mapping you can point me to, specifically for configuring the SMO20 in emonCMS? Do I need additional third party hardware to accomplish this?

sensor.ashp_power
sensor.ashp_total_active_energy
binary_sensor.espaltherma_3way_valve_on_dhw_off_space
sensor.espaltherma_flow_sensor
sensor.espaltherma_inlet_water_temperature
sensor.espaltherma_leaving_water_temperature_before_buh
sensor.espaltherma_lw_setpoint_main
sensor.outdoor_temperature

Thanks,
Samir

dMb · 18 May 2025 19:49

Hi Samir,

That’s a great approach. It would be different if this was October, or February…

My thinking is that we make sure your DHW is working robustly then bring the space heating back into the equation and get that optimised too, well before winter.

Yep. I’ve found the best way to achieve that is to change HEAT PUMP > OP. MODE (Menu entry 4.2) to “manual” (it’s probably set to “auto” currently). Basically that means it will keep doing DHW as normal but won’t attempt any space heating until that setting is changed back to “auto”.

Like you, I want to force DHW to run in the off-peak tariff period, so my DHW schedule (Menu entry 2.3) looks like this:

Effectively that’s saying:

It’s not allowed to heat any DHW between 04:30 and 00:30 - no matter how cold the DHW tank gets
At 00:30 it’s allowed to start heating DHW, for which it will use the default “Comfort Mode” set at Menu Entry 2.2
At 04:30 - even if the DHW tank hasn’t reached its target temperature - it will stop heating DHW

I suspect your current settings are simply over-riding the default Comfort Mode, rather than ‘blocking’ the heating of DHW.

The myUplink API authentication that the Home Assistant integration relies upon is either set for Read-Only or Read-Write access. I think you’ll have to create and use a new API Key if you want to change that to Read-Only.

All I really meant by my previous comment was for you not to try to make configuration changes via Home Assistant, but if you think there’s a significant risk of that happening accidentally then forcing Read-Only might be a good way to go.

That 30% is configurable. The puzzling thing is the charge pump running at that level means it was ‘expecting’ to do some space heating (which also aligns with negative DM value). So something odd is happening with your space heating configuration - but let’s get your DHW sorted first then look at space heating later.

To fully participate in heatpumpmonitor.org (via emonCMS) you will need a third party electricity meter on your heat pump electrical input and a third party heat meter on your heat pump plumbing circuit - a lot of people use something like Level 3 Heat Pump Monitoring Bundle (emonHP) - Shop | OpenEnergyMonitor but there’s a significant cost for the components (especially the heat meter) - plus the cost of installation.

For a more limited set of parameters sourced from myUplink (via Home Assistant) those could be integrated without any additional hardware. Since you’d be missing some of the inputs typically provided to the “MyHeatpump” your system wouldn’t be listed on heatpumpmonitor - but you could make your emonCMS graphs visible to others. You’d need to pay for an account on emoncms.org to do that.

An alternative approach is for you to (temporarily) grant other registered myUplink users read-only (“Viewer”) access to your system on myUplink, so they can see your data there - but not make any changes.

David

samirrpatel · 18 May 2025 20:22

Hi David,

I’ve just made the switch to manual op mode. I assumed I should untick “addition” and “heating” which were both initially ticked when I entered manual mode.

As for the blocking schedule I made the suggested change to schedule “off” periods earlier this afternoon. I made the change just after my wife had been for a shower at around 1545 but strangely the data being shown via myUplink seems to indicate no drop in the water temperature at that time or thereafter. Usually I can see when showers have been taken as the hot water top value drops but today it’s a flat line after the tank was reheated following showers we had earlier in the day. I’m hoping that’s just a side effect of me making the scheduling change just after hot water had been used (i.e. perhaps the system isn’t even reading any sensors until it kicks back into gear at midnight?). I’m very much hoping that’s the case as my wife did have a longish shower and I think I’ll end up having a cold one before work in the morning unless the DHW comes on tonight! I’ll be fast asleep by midnight so will find out in the morning.

I have two scheduled periods designated for heating water, the first of which is shown below and seems to match your settings. Schedule 2 covers 1630 - 0000 (thus allowing the heat pump free reign between 1530-1630)

One thing I did notice as I was moving through the menus is the heating curve setting which looks like this (although there are also further settings labelled “own curve” which might be overriding this and are the temps at those 7 points I previously mentioned)

Fingers crossed for hot water in the morning!

Thank you for all your help, it is greatly appreciated and I feel like I’ve already learned a lot about my system this weekend!

Samir

samirrpatel · 19 May 2025 06:39

Happy to report I had a hot shower this morning at around 0615 and the DHW kicked in just after at 0618 and ran til 0707 (assuming that 7 minutes is just a lag in the reporting) after which it turned off. So this all sounds in line with what we had hoped. I can also see a “hot water mode” value which I deduced to have different values depending on what is being requested wrt DHW (-1 = blocked / 0 = economy / 1 = normal / 2 = luxury / 3 = immersion).

I’ll give it a day or two like this to iron out any issues and observe what happens during the 1530-1630 window, then decide if we need to think about any other changes wrt DHW. One thought is to switch it to “Luxury” to get the tank hotter (so after mixing we get a larger volume of ‘useful’ hot water) but I’d only want to do it during the off-peak window and not in the hour slot in the afternoon. I don’t think this is possible via the blocking schedule but perhaps could be achieved via a Home Assistant automation.

dMb · 19 May 2025 07:56

Hi Samir,

Excellent!

Correct. Your photo looks exactly like my configuration for “DHW only” mode.

I don’t need to use “schedule 2” so wouldn’t be certain what to set there, but my hunch would be exactly what you’ve done - with the 07:00 - 15:30 “off” period in “schedule 1” and the 16:30 - 00:00 “off” period in “schedule 2”.

That’s my understanding too and would be a good use for Home Assistant (to change the ‘default’ between Economy and Comfort between the two allowed heating periods). If for some reason the HA integration fails to make the change, you’d still have hot water.

Well, that Heating Curve is miles out… and I’m pretty sure you’ve found the reason for the Central Heating preparing to run the other day (and hence running the charge pump).

For comparison, my 1.9.1.1 looks like this:

While you won’t want to use the same settings as me (I’m fortunate to have a very highly insulated house, which is why I can get away with Curve #6) you’ll want a profile that looks a lot more like mine. I can’t quite make out what Curve number your photo is showing; the factory default is Curve #9.

You may have the original settings in your Home Assistant history but otherwise the SMO 20 user manual gives some guidance on making changes (and reminds me that “Own Curve” is only used when selected as Curve #0 in 1.9.1.1).

You’re very welcome. It’s clear that you’re picking things up quickly. The NIBE units are good but if the installer leaves them on the default settings they generally don’t fulfil their potential, so it’s always useful to understand the data enough to optimise the settings a bit.

David

samirrpatel · 19 May 2025 21:07

Bingo! Ok, so now the only thing I need to try and figure out is what it was originally set to and how it might have changed. Looking in HA history it seems to suggest it’s always been on “curve 15” but I’m not sure I should trust that. Is there somewhere in the SMO20 where I could see what it was historically? When I setup myUplink I think I took a backup of the settings but I’ll need to figure out what I actually did with that.

samirrpatel · 20 May 2025 06:09

I found that old backup (not that old, from 5th April 2025, which was when I applied a firmware update to the SMO20 to allow me to setup myUplink)

It’s in a file called STORE.set and contains the following data. I think 47007 is the curve (which I currently see as 15) and 47011 is the offset (which I currently see as 7)

I’m not sure what the format of this file is yet but there seems to be two possibilities for the curve, either 12 or 9 and the offset seems to have been 0. Do either of those combinations seem plausible?

[NIBS;20250405]
47007 12 9
47011 0 0

dMb · 20 May 2025 06:38

Hi Samir,

I’m not familiar with the format of that backup file either, but 9 is the factory-default Curve and 0 is the factory-default Offset - so those are by far the most likely original settings.

I know you said your installer isn’t being especially responsive or helpful, but they might have some records of which Curve they originally set - or might remember if they changed it from the factory-default setting.

Starting with Curve #9 (or #10) and an Offset of 0 would seem sensible to me.

David

samirrpatel · 20 May 2025 06:52

Thank you. Yes, I’ve dropped the installer an email to see if it’s my lucky day and he responds, but failing that I’ll switch it to 9/0 and give that a go. Presumably there is potential for further optimisation thereafter as we see the data come in.

To be honest right now there is no need for heating anyway. Is it better to just leave things on manual with no heating enabled for a long period (i.e. the summer) or better to enable the heating again but configure it such that it doesn’t really do much during these warmer months?

dMb · 20 May 2025 07:18

My recommendation would be to re-enable the heating (once you’ve set the Curve and the Offset) - to check it’s behaving itself. There are some other settings that can be tweaked, to control whether the charge pump runs or not, based on the outdoor temperature. Once you’re happy the heating will work OK when you want it to, you can then swap it back to ‘manual’ for the summer - to save the heating coming on if we get the odd cool night.

Absolutely. But you’ll need to see if the house gets too warm or too cool in different outdoor temperatures before finally choosing the Curve and the Offset, so there’s not much more you can do before Autumn.

Do you have the optional indoor temperature sensor (BT50)? If so, that makes the choice of Curve less important, since the control algorithm will make adjustments if the measured indoor temperature is above or below the set-point. Without that sensor, you’re entirely reliant on the choice of Curve and Offset to manage the indoor temperature.

David

dMb · 20 May 2025 09:26

Hi Samir,

Here’s a basic summary of how the NIBE heating control algorithm works, for an SMO 20 or similar controller, to help you assess whether it is indeed ‘behaving itself’:

It knows what the (short-term average) outdoor temperature is from sensor BT1
It ‘looks that up’ against the selected weather compensation Curve and Offset to derive the Calculated Target Flow Temperature S1
- That’s the Flow Temperature which is expected to precisely offset the heat loss from the house, when the weather might be cold but isn’t especially sunny or windy
Some houses get significant passive solar gain, or have other variable heat gains or losses due to e.g. cooking or draughts so the indoor temperature from optional sensor BT50 can be used to adjust the target flow temperature based on whether the indoor temperature is above or below its set-point
- This results in an adjusted target S1 that is higher or lower than the WC Curve specifies, to allow for those external effects
A variable-speed compressor motor can modulate its output to a certain extent, but can’t always exactly match the calculated target flow temperature S1, so the actual flow temperature from sensor BT25 is used to ‘audit’ how well the system is performing against that target
- If the target (S1) is e.g. 35C and the actual (BT25) is 33C, that’s a 2 Degree ‘deficit’ - and for every Minute that 2 degree deficit persists the algorithm will subtract 2 from the Degree Minutes (DM) counter - so the DM value is effectively a cumulative record of under- or over-shooting the calculated target flow temperature
- If the heating demand is low, the compressor will need to cycle on-and-off (because its minimum output is greater than the heating demand) so when the compressor is off the DMs will become increasingly negative until a configured threshold is met and the compressor starts
  - This also applies when the unit has switched over to heat DHW (or to run a defrost cycle) - the central heating will have ‘missed out’ on some DMs while the heat was going elsewhere, so the DM value tells it how much ‘catching up’ is required
- With the compressor running, the actual flow temperature (BT25) will be greater than the calculated target (S1) so the DMs will become less-negative. Once the DMs reach 0 the compressor stops - but there’s still heat in the heat exchangers so the DM value typically keeps increasing beyond 0 (though it’s capped at +100) before decreasing again as the ‘deficit’ starts to build up again.

Hopefully that explains where the DM values come from (and how suddenly getting the large, negative DM value you saw the other day is most likely a spurious data issue).

A few further points:

There needs to be a bit of flow past sensor BT25 in order for it to give an accurate reading, hence the variable-speed circulation pump (or 'charge pump’) runs at a low level even when the compressor is off - and then runs faster when the compressor is on, aiming to maintain the target delta-T between the Flow and Return temperatures
- The circulation pump shuts down when the outdoor temperature is warm enough not to need heating
The Degree Minutes control mechanism dates back to before variable-speed inverter-drive compressors were a thing, when the compressor had to cycle on-and-off and the controller needed a robust mechanism to determine the on-versus-off durations while not doing too many compressor starts
- NIBE then retained the Degree Minutes mechanism when they added variable-speed compressors. I believe Vaillant use a similar mechanism.
There’s a configurable ‘compressor Curve’ which governs how ‘hard’ the compressor motor gets driven by its inverter, once the heating demand is above the compressor’s minimum output
- If this curve is set ‘perfectly’ the DM value should stay slightly-negative (-50 or thereabouts) for long periods while the compressor is running
If for some reason the actual flow temperature (BT25) fails to reach the calculated target (S1) - even with the compressor running at full speed - the DM value will go more and more negative so there’s another DM threshold setting which can bring in an auxiliary (pure resistive) heater to help out
- It’s possible your rogue Curve with its target of 63C was getting into this territory

I’ll stop now. That’s longer and less ‘basic’ than I’d intended - but hopefully it all makes sense.

David

samirrpatel · 20 May 2025 17:50

That makes sense. I’ll do this tonight and report back what happens tomorrow (hopefully not a lot wrt heating!)

I don’t think so. If I did would it need to be located somewhere it could reliably determine the average temperature of the whole house? We do have heatmiser thermostats in each room controlling the UFH but I suppose there is no direct feedback from those to the AHSP

samirrpatel · 20 May 2025 18:04

Incredibly grateful for you putting this together. I’ve only read through it once and will need to do so a few more times to wrap my head around it all but I think it’s really well explained and makes a lot of sense even on first pass. I’m sure this thread will also be invaluable for others who have NIBE systems and are trying to figure out how best to set them up.

No response from my installer, unsurprisingly, but I feel like I have the general knowhow to navigate this without his input now that you’ve been so very helpful!

I wondered if there was any sensible “monitoring/ early warning” indicators that one could setup to flag issues. E.g. detect “your charge pump is regularly doing XYZ when you’d expect it to be doing ABC” or “sensor XYZ is reporting lower than expected readings given ABC and DEF”. I’m assuming NIBE doesn’t provide anything like that but perhaps it could be built in HA. Would love to hear your thoughts on whether this would be worthwhile/easy to implement.

Thanks,
Samir

dMb · 20 May 2025 19:45

That would be the plan, yes. My sensor is on the first floor landing of a 3-storey house, which only has a north-facing window and doesn’t get any direct sunlight so does a thoroughly decent job of reporting ‘average temperature’.

In my case the indoor sensor is useful because the house can (intentionally) get many kW of passive solar gain on cold-but-bright days in winter, which would make it overheat on pure weather compensation control. If you don’t have that “problem” it’s much less of an issue.

If you do happen to have a suitable sensor location with an accessible wiring route back to the SMO 20 controller, it’s easy enough to retro-fit an indoor sensor.

Indeed. If my outline of the control algorithm proves useful it could form the basis of a more comprehensive overview, with added references to where in the menus various settings can be adjusted.

I’ll give some thought to that. NIBE have various built-in alarm events that can get triggered (and are reported in real-time via myUplink) that alert on error conditions, so I think NIBE systems are already ahead of the game on that front - at least for ‘proper’ errors. People who have third-party electricity and / or heat meters also get a sanity-check via the readings from those.

Thinking about issues some other forum members have reported, there are definitely some ‘implausible’ combinations of sensor readings - such as the DHW tank temperature being significantly lower than the Return temperature to the Heat Pump, at the end of a DHW cycle. Several of those have been traced back to poor installation of the tank sensors (without thermal paste).

David

etchelsa · 21 May 2025 16:19

Hi Samir

I’ve joined this thread a little late..I like to try and help fellow Nibe users so have jumped in!

There is not a lot I can add to the space heating part and it seems this is on the path to resolution / understanding

With your space heating it would be useful to know your setup in terms of buffer tanks and any secondary circulation pumps you might have and what triggers those (run 24/7 or via room stats etc). There is a setting to control if the charge pump runs only when a space heating demand is present (via degree minutes) or at all times. Depending on the plumbing you might need to change this. David mentions it needs a flow past BT25 but you could have a secondary pump doing that for you. I found my charge pump was circulating water outside and back through the f2040 which had an unnecessary heat loss and triggered heating cycles more often than I needed

Nibe has a fair few settings that do seem to need optimising based on the plumbing so I’ll keep an eye on updates and see if I can offer anything I have learned when optimising my space heating.

samirrpatel · 21 May 2025 20:22

Hi Sam,

Thank you for your willingness to help!

Did you mean DHW rather than space heating here? I do think we’re well on the way to resolving that issue. The blocking schedule appears to be working well. I’ve got a couple of ideas I wanted to explore when I get time to tinker:

can I use HA/myUplink integration to switch the hot water mode to Luxury during the off-peak period and back to economy for the peak so I minimise peak usage
could I create a manually triggered automation that could cancel the peak scheduled DHW window for the day. E.g. if I know we’re not planning to have showers after the scheduled peak heating window (1530-1630) on any given day then I trigger the automation and make the system wait for the overnight off-peak period before heating up the tank. It would have saved me ~35p today so not a big saving but I’d still like to reduce my bill and do my bit for the environment if I could.

I knew it was only a matter of time before my ignorance of what I actually have would be exposed. I’m just going to come out and say it…I have no idea what a “buffer tank” does but I know a picture can tell a thousand words, so here is one! In the bottom right is one of three heating manifolds that control the UFH (we have one of these on each of three floors in our town house). As to whether I have a buffer tank or not, not to get too technical but I have one small white tank and one small red tank. Is one/both a buffer tank?

I updated the heating curve to #9 with 0°C offset yesterday evening and I don’t think the heating has turned on today and nor has the charge pump gone crazy as it was doing when I started this thread, so that is a good sign.

Thanks again for your offer to help!

Samir

etchelsa · 21 May 2025 21:53

Yes that curve you originally had would definitely have caused you the problems you were seeing.

Your set up is pretty much the same as mine and you have a buffer tank. It’s the larger white one on the right.

Have you put your operating mode back to auto? If not no space heating will occur irrespective of the curve you chose.

There is quite a bit I learned when optimising this type of set up and happy to step through it. It depends what problems, if any, you have with space heating. A bit hard to tell with summer upon us.

How new is this installation? Have you ran it through a winter season and had ok comfort levels? Have you been happy with usage / bills?

And just out of interest what sized unit are you running for a 3 floor town house? Is it the f2040-12 (12 kw version)

samirrpatel · 22 May 2025 06:02

Thanks. I’m assuming the buffer tank is used by the heating system? Out of curiosity what do the smaller white and red tanks do then? Are those for safety?

Yes, it’s back in auto mode

It was installed 2021 so it’s been through 3 winters and each time we’ve made tweaks to increase comfort. The first winter was freezing cold. We had the installer back out and he tweaked some settings which I think we’re mostly around the UFH and that helped but the second winter was still cold, though better than the first. The winter just gone was the most comfortable although on particularly cold days we’d still like it 1-2°C higher. In terms of bills I’d say they have been very high, although we have been on a standard tariff until recently so it’s probably not comparable to what we will see this winter (we’re on Eon NextDrive now). We don’t have solar and we’ve only recently got a fully electric car (previously we had a plug in hybrid). Getting the fully electric car prompted us to switch tariff but we possibly should have switched sooner. Previously we didn’t think we’d benefit from having dual prices as we felt the heat pump needs to run all day and so would be more expensive to run on peak electricity. Car usage is minimal, call it ~15 miles most days. Maybe our assumption on heat pump running costs was incorrect, but we’ll probably only find out this winter.

Quoting from a document the installer provided:

One Nibe F2040 16kW R410a ASHP unit and a 300 Ltr unvented storage cylinder with buffer vessel, primary circulating pump, plant room pipework, insulation, controls, commissioning.

B. System Design
We have completed room by room heat loss calculations for the property based on the architect’s
drawings and meetings, which shows there is a requirement for a heat pump with an output of
approximately 10 kW at the design ambient temperature. The Nibe unit selected is a 16 kW unit. At
-1.8°C the unit is capable of providing 12 kW.
The unit will provide the required output down to -15°C. This allows for the provision of 100% of the
space heating and domestic hot water for the new dwelling. The assumption is based on the
information on the properties EPC and our discussions.