The immersion control switch box
The DHW cylinder.
Buffer vessel
View of connections to DHW cylinder
I program the DHW every afternoon after Agile rates for the following day are published using the SMO20 scheduling on the MyUplink app.( I find this app rather cumbersome to use - setting times is rather like watching an old fruit machine whirling round and always not lining up with three bells in a row! The old Uplink app was much easier to use). I did have the system connected via an Octopus R&D labs integration to Nibe Uplink which (theoretically) allowed the DHW and heating to be automatically controlled according to preset rates depending on Agile prices. However the link depended on an API to Uplink, which was very unstable and kept logging out, and ultimately as another unforeseen consequence of the “upgrade” to MyUplink, this integration is now impossible as MyUplink is not supported by the Octopus integration.
I also program my battery (I have solar plus a battery) at the same time. In late autumn/winter/early spring I charge the battery from the grid when it’s cheap - by cheap I mean usually less than 15p per kWh. Although as long as it’s less than the Octopus peak rates for the day I may charge it. This enables me to run the house off the battery during Octopus Agile peak rates which are usually 16:00 to 19:30 ish every day. I have also been knocking back the heating during this time using the scheduling on the SMO20, although this schedule has not been run over the last week or so as I decided that I’d rather spend a few bob extra and keep warm in the evening.
1 Like
I know all sorts of IFTTT integrations are available/possible but I am reluctant to go down the RasberryPi/home assistant route.
Thanks for the photos and the extra info on scheduling etc.
From my understanding, “delta temp” is the recommended setting for your DHW plumbing set-up (heating coil inside a DHW cylinder) so that’s a good change to have made and should impact the behaviour during a DHW cycle (for better or worse! 
). It will be interesting to see what subsequent graphs look like.
The photos of your DHW cylinder show a black wire going to the sensor pocket just above the big red label, whereas the lower sensor pocket (above the immersion heater) is empty. It would be good to confirm whether that black wire is cabled to what the controller sees as BT6 (“Hot water charging”).
- Are there any other sensor pockets with similar black wires elsewhere on the DHW cylinder, out of shot, which might be BT6?
- If not, that implies the visible wire must be BT6 - in which case I think it’s too high on the cylinder
- Personally I would have put BT6 in the lower sensor pocket - in the vicinity of the internal heating coil
- Do you also have a BT7 (“Hot water top”) sensor showing values in MyUplink?
- My installation has BT6 in the lower sensor pocket and (the optional) BT7 in the upper sensor pocket, which gives more info on how much of the tank is ‘hot’
1 Like
Very interesting. There is no BT7 sensor on the system. There are 2 “control stat” holes on the DHW cylinder:
Top
Bottom
1 Like
Thank you for the photos, it looks a neat and tidy installation and much better than mine!
I had the same observations as David about the temp sensor (if it’s BT6)
I’m not seeing anything obvious from the install but something is obviously causing your HP to cycle. The earlier graphs show the flow and return temperatures have very little difference and suggest the heat isn’t being lost into the cylinder water for some reason. perhaps this is causing it to cycle. Although your earlier posts show it does work sometimes? Does it always cycle in lux mode? And always work as expected in normal mode? Out of interest why do you schedule lux mode? Do you have a high hot water demand compared the size of the cylinder (it doesn’t look overly big)
If you’re not scheduling DHW to “off” and leaving it at “normal” mode outside cheap agile rates, there is nothing really stopping it wanting to charge up the water anytime of the day - depending on usage and the target temp / delta temp algorithms.
I think it might be beneficial, if possible, to build up a wider picture of when cycling occurs vs when it doesn’t. Is it everytime DHW is charged in lux mode at night?
1 Like
Thanks for confirming, so that is BT6 we can see in the photos and Sam and I are both of the view it is “too high up” - so it would be beneficial to move it to the lower sensor pocket (or turn the existing one into BT7 and add a second, lower sensor to become BT6).
That raises the question of whether the people who installed your system are still around and being helpful. If they are, I’d be inclined to ask them to make that change - not because it’s difficult but more to keep them on-side with ‘owning’ the installation in case there are other issues they need to fix.
(To move the sensor yourself you would need some thermal paste and maybe an extension to the sensor cabling.)
1 Like
Thanks - very helpful advice indeed. The hot water control reversing valve (red valve) is a Nibe VST 05. Do you know what the difference is between the VST 05 and the VST 11? I have just been reading the installation manuals to double check the details of the temperature sensors and noticed that the 12kW version of the F2040 specifies using the VST 11.
Interesting. I’ve done quite a lot of work with the NIBE Uplink API and it’s very picky in terms of Authentication (especially the OAuth2 Token renewal requirements) but I’ve found it to be robust. MyUplink has a broadly-equivalent API, but with a different set of API calls that Octopus would need to code against. (I’d hope that’s in their plans anyway since NIBE want to kill off NIBE Uplink once they’ve migrated everyone over to MyUplink.)
The wider topic of Home Energy Management / Optimisation is a huge challenge (but fascinating - or maybe that’s just me 
). Time-of-Use Electricity Tariffs + Heat Pump + Solar PV + Battery (+ maybe an EV to charge) is a complex set of interconnected systems - heavily influenced by the weather (cold but sunny tomorrow???) and how a building responds (passive solar gain? high thermal mass?) and how enthusiastic the occupants are about saving money.
1 Like
My understanding is:
- VST 05 has 22mm pipe connections and is rated for a maximum of 11 kW
- Further info here: https://www.nibe.eu/assets/documents/14514/031586-3.pdf
- VST 11 has 28mm pipe connections and is rated for a maximum of 17 kW
- Further info here: https://www.nibe.eu/assets/documents/9828/011023-11.pdf
So that checks out: 12 kW is nominally just higher than the maximum capacity of a VST 05, so a 12 kW ASHP would ideally want a VST 11 (and 28mm pipework?).
1 Like
Re the control valves - that’s what I thought. The pipe work is 22mm I believe. Not sure whether this is significant in terms of performance as I’m not a heating engineer!
Key phrase is “how enthusiastic the occupants are on saving money” - bear in mind this installation is in Yorkshire 
This might be a false / terrible theory as we don’t yet have further information to debate, however…
- we know from the data you have sent to date, your HP cycles on “lux” but doesn’t cycle on “normal”.
- David points out ”lux” will use additional heat, which would be the immersion heater for DHW
- the immersion and flow/return/coil seem to be co-located at the bottom of your cylinder and the BT6 sensor is at the top
So I wonder if…
The “lux” setting is pulling in the immersion because BT6 isn’t seeing a rise in temperature quick enough due to its position at the top of the cylinder.
The immersion is heating the local water around the coil and therefore the heat isn’t transferred particularly well into the cylinder. The result could be that the return temperature is very similar to the flow when it gets back to the HP. This small delta T causes the HP to shut off (cycle).
The above process repeats until the immersion gets the top of the cylinder hot enough to satisfy BT6 and the DHW algorithm. This doesn’t explain why we see your HP stop and BT6 continues to rise but maybe there is an element of eventually giving up in the Nibe control software.
Perhaps you could do one of two things and report back:
-
run all DHW on “normal” mode and see if you get cycling
-
switch the immersion to “OFF” on the control box and leave it on “lux”
The second option could run the risk of no DHW. You can of course switch to “ON” and get it heated up to recover the situation.
Perhaps do this in a day or two once you have assessed the change you made for “target temperature” to “delta temperature”
This could all be very far away from what is happening…
1 Like
Many thanks again! I’ve set the DHW to normal - I’ll let you know how it goes…
1 Like
This home energy management is something I want to progress for the next heating season - I’ve still got my installation problems to fix first but am waiting for when I am less reliant on the heat pump (just in case it all goes wrong)
I’ll probably spin up a new topic soonish to discuss and look at “smarter” control of a Nibe system!
1 Like
I’d be very interested in ideas on smart control for a Nibe system - I suspect most of the grid pricing capability is already built-in but because we’re in the UK it isn’t activated in the software.
Really appreciate all your ideas and help on this
2 Likes
There is certainly some ‘spot pricing’ functionality built into the ‘smart energy source’ feature of the SMO 20 controller, but like you say it doesn’t come up as an option for an installation in the UK.
To be fair to NIBE, it’s tough to decide how a NIBE SMO 20 controller should be expected to know the ‘spot price’ for electricity in the UK. In theory a SMETS2 meter knows the current tariff (and that would be electricity supplier independent) but that’s a tough integration to implement - and far from universal (i.e. not everyone in the UK has a SMETS2 meter yet) - and ideally it would want to know the future pricing, not just the current pricing. The SMO 20 controller hardware hasn’t got the horsepower to talk to something like the Octopus API - and I presume NIBE wouldn’t want to lock-in to a single electricity supplier like Octopus anyway.
1 Like
Latest progress, running DHW on Normal comfort mode; have just (around 10:45 - 11:00 ish) seen an alarm (info) code on the control panel - 162 High condenser out. This coincided with the heat pump running DHW (see photo).
Extract from Nibe technical manual re. alarm code 162 troubleshooting guide.
I just happened to be in the garage when the alarm code appeared on the SMO20 screen - as I said previously MyUplink doesn’t give access to the warnings log, even if you pay for the extra subscription for History. This is the same code as I was seeing previously before the software update to MyUplink.