Daikin Altherma, ESPAltherma & Home Assistant with OpenEnergyMonitor

It is interesting that you have got good correlation between the Daikin temperature sensors and the MID meter.

My “calibration” testing shows that three different Daikin sensors - which should be measuring the same temperature of water flowing around the system without heating - have a spread of 1.8C. @John had a spread of 1.9C and @Stephen_Crown about 0.9C (I think)

Maybe we were all unlucky, or you were lucky :grinning:

Or maybe the 4-8kW units have a better temperature sensor location and insulation than the 9-16kW units.

@MBC @squarepeg77 @matt-drummer I just had a call from Daikin L2 support, following my email of 12 Dec (long story!) asking

  • if the huge difference between R1T and R2T was “normal”
  • which sensors the MMI used to determine LWT, dT and Energy produced.

He was helpful, but had no idea why the discrepancy, and rather than suspect the thermistors, he suggested there might be some piping problem (?). So he’s set up an engineer visit sometime in the next few weeks to check it all over. This isn’t urgent - I’d rather they were fixing someone’s HP that isn’t actually working! I don’t think there is a piping problem in the HP, that would be a glaring manufacturing error, whereas a dodgy thermistor is much more likely, especially as others see similar variations. But hey, it can be checked.

Which is a start…

In the light of the minimum power drain of ~900W vs. 4-4.5kW output, I’m also wondering if I need the EDLA08 rather than the EDLA09. I’d have to get an alternative HLC, and/or show my data from the cold snaps, all of which is possible, to convince Octopus to swap it. But then I’d want to be sure the smaller one would do the job!

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I had a visit from a Daikin engineer today.

He installed new firmware on the outside unit that is supposed to help the response time of the expansion valve.

I also reported my concerns about the inlet water tape heater that I mentioned here:

The engineer has fixed the wiring for that. It sounds like some jumper or connection was set incorrectly.

I disconnected ESPAltherma before the engineer visit, so as not to freak him out. :smile: I’ll reinstall it over the weekend and see if I get closer correlation between R4T and the other sensors. I have a suspicion that the tape heater on the outlet of heat exchanger might also be enabled…

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If you think it is oversized just call octopus and tell them what you are seeing. If you are able to I would look at doing your own survey with heatpunk (free online tool) first as that will help you see where you are at.

Ideally you would want to check not only the overall heat loss but also the heat loss per room as if they missed something like loft insulation you may need to swap radiators to have a balanced system (depending on the accuracy of the first heat loss survey they may even offer to do this like they are with mine). That is part of the reason they re designed my system to work at 40°c and they actually accepted my recommendations for the replacement radiators as the design team went from no loft insulation to loft and insulation between floors (I have no insulation between downstairs and upstairs just 600mm in the loft).

If you are able to afford to have a heat geek in it does offer peace of mind but there will be a cost of this (for me it was well worth it and Szymon is amazing). Although in fairness Octopus offered to swap the heatpump based on my OEM data and my heatpunk calculations I just wanted to wait until I was certain and for me that was a full heat loss survey from a Heat Geek.

Am I the only person who wants to pop a small clown and balloon in the heatpump so the next engineer to open it has something ‘interesting’ to see :grin:

I wouldn’t be concerned that going from a 9 to an 8 kW heat pump might not be large enough to do the job. In this country we are required to design for the worst temperature we are likely to see while maintaining 21 degrees. In Europe, where some countries are 20 years ahead of us with regard to heat pumps, they design for typical winter scenarios and accept that occasionally, they will need another jumper or to light the fire for some additional heat.

There are so many variables to heat loss calculations that there is a large margin for error built in. Go for the 8 and enjoy lower minimum power usage of around a third of your 9’s.


Hi, I’ve got a Daikin 11kw ASHP running my underfloor (130ms). 4 towel rads and 6 rads upstairs. Hot water is on completely separate system the Ariston 250i plus ASHP cylinder. I’m insulated to the max 900mm in all loft spaces, insulation in between the joist walls. I’ve got AS on weather dependent. My COP isn’t that great I can’t seem to get over 3 and when the temperature drops 4 or below my COP is 2. My main issue when it drops to 4 or below is the defrost cycle my daily consumption in the winter jumps from between 40-50kw to a 100kw per day? I’ve rang Daikin up and spoke to technical and there saying I should increase my Buffer Vessel from 20litres to 100litres so when it is in defrost cycle I’ve got a bigger back up? Is that efficient and economical ? Is there any other ways of sorting this problem? I’ve tried running flow rate at 35?

Personally I would start by using heatpunk and checking your heat loss (or get a heat geek in to do this if you don’t mind paying).

That system sounds extremely poorly and like something is very wrong.

I know my local heat geeks can come and review other installations (for a few obviously) and make recommendations for improvements and I fully recommend this as it helped me get mine from a COP of 3.2 up to 4.5-4.8 (it also involved the original installer replacing the 9kW for the 8KW as the heat loss was incorrect)

Also from my experience the 9,11 and 14 kW Daikins are just software derated 16kw so have no lower end modulation and output a minimum of 4.5kw and take at least 920w of power. Add in a bit of a configuration issue and it is easy to see how your system is this poorly.

The 8kW while in name ‘not much different’ is the biggest of the “small” 4,6&8kW units and as such has far superior modulation and has a minimum input power of about 270w. This now runs all day and night ticking over.

Check out Farnborough, Hampshire for the difference between the start of January and anything past the 15th, you will see what I mean.

How much does it cost for heat geek to come round and do an inspection?

Heat geeks are usually independent companies with specific low temperature heating design training so the costs may vary by area / person.

I am in the south east and it was £360 for a full heat loss survey and while Szymon was here he had a look at the setup and gave a few pointers.

The heat loss survey helped to show the radiators needed for a 40°c flow temp so I am getting them swapped by the installer too.

For what you get and the experience these guys have it is usually a pretty good deal and to be fair looks like you could save more than that over the course of a winter with that install.

I would just ask them to provide whatever advice in an email or in writing as you can then go back to your installer with some hard proof from an independent engineer.

If you Google ‘find a heat geek’ and give the local one or two a call and ask the question. Only a few minutes of your time to loose so worth a shot.

Even with an access point within about 4 feet and just behind a double-glazed window, my m5stickC’s connection is still incredibly ropey inside the faraday cage of the monobloc unit, this outdoor box looks an ideal solution.

Would you mind giving a little more detail about how you put this together, I’m a bit of a novice when it comes to some of the electrical connection stuff and so would appreciate some pointers.With the CAT5 cable did you just crimp some dupont connectors on to the individual wires? Are you using Dupont connectors at both the X10A port and ESP or did you use a JST-EH connector for X10A? Any suggestions as to where to get the stuff as I keep finding places that want me to buy a minimum 100-pieces, which fells like a bit of a waste :grin:

I am popping mine inside the outdoor consumer unit. There is already room for the cables in the conduit to help heat pump and I have the JST-EH crimp tool so putting a plug on one end and some pins on the other shouldn’t be an issue.

I will be turning off the power at the main breaker first and obviously don’t open the consumer unit if you do not know what you are doing with electrics as they can bite.

If you want a length of crimped cat5 let me know.

Honestly that would be absolutely amazing. As I’d be buying a job lot of connectors and crimping tool(s) for a single cable. As it’s a bit of a custom job I can’t really find anywhere selling the length of cable with JST-EH header that I need.

My outdoor consumer unit is a few metres away, so I wasn’t planning on housing the ESP in there. Instead I’d like to route it through the cable paths out of the monobloc and attach to the outside, similar to tiger_cook.

If you were able to make-up a 1m CAT5 cable with a JST-EH connector at one end and Duponts at the other, I’d be eternally grateful. :pray:

For anyone coming across this at a later date - on the ESPAltherma page, the author suggests the use of a 2.54 female long header. I ran some phone cable from the heat pump into the house beside the cylinder to ensure no wifi problems and used pre-made 200mm dupont jumper cables (ebay then cut in half) with jelly crimps (which just close up using pliers) each end.

Granted the JST-EH connector is the neatest solution but there are other ways too is all I’m saying.

@John @Stephen_Crown

I have some new data following the visit from the Daikin engineer’s visit on Friday.

As soon as I re-installed ESPAltherma, it was clear that the temperature readings were making much more sense.

I now get very good agreement between R1T, R2T and R4T. Here’s the new “calibration” run:

The values are within 0.2C of each other - down from a spread of 1.8C! :partying_face:
So, from a sample size of 1, the thermistors are pretty good.

I am now convinced that two tape heaters E11H (inlet) and E12H (after heat exchanger) were active whenever the water circulation pump was running and they were significantly distorting the R4T and R1T temperature readings.

I’ve been running the pump at “60% limit when sampling” and used to see the pump using about 128-132W when circulating the water overnight to prevent freezing. I’m now seeing 66W usage, a reduction of 66W, which matches 33W for each of the two tape heaters.

I don’t know why the tape heaters were configured this way and the engineer was vague on what he did, other than “check the wiring, and fix it”. It’s not clear to me whether the units were manufactured this way deliberately, accidentally or if it was some change that was made during installation. I’m going to report back to my Daikin contact and see if this is a systematic problem.

I’ve got some photos of the X7M connector where the heaters (initially) connect, but only after the engineer’s visit. I don’t know if that’s what he fixed, or elsewhere. Let me know if you want to compare.

I am also seeing much better performance since the change:

  • I ask for a delta T of 4C, and I get it (once the pump has settled)
  • the pump speed is higher - up from ~12l/min to more like 16l/min
  • COP is around 20% better* (still not stellar performance from my system with small-ish rads, but much more in the realms of what I think is decent performance)

I’m going to go and experiment with other settings now (fancoils instead of underfloor, dT 5 instead of 4, tweaking flow rates etc.) to see how much more efficiency I can extract. Heck, I might even try the Madoka with some mild modulation again!

@John since you have an engineer visit booked, I’d definitely see if you can persuade them to investigate these tape heaters.

If you are prepared to remove the heat pump cover again, the inlet tape heater is the orange/red tape here:

It showed up nice and hot on my thermal camera, but was also noticeably warm to the touch.

*The Daikin engineer also installed some new firmware, but my gut feeling is that the fix for the heaters is the dominant factor


That’s exactly what I see too.

That’s great that you’ve been able to go to the next level of detail on this issue. :clap:

I shall take the cover off mine and see what’s going on as well as I have a Flir One camera.

It seems like there is a logic bug that’s made its way into production systems. It happens (I work in IT so see this kind of thing a lot), but obviously shouldn’t.

I wonder if enough of us complain then they’ll address the issue.

I figured it was a (software) logic bug too - I’m a SW guy, so I know who to usually blame :rofl:

However, I think from the way the engineer spoke about it that it was a hardware - wiring - issue.

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Haha yeah me too, I’ve been speculating about BUH/no BUH code “features”, but perhaps it is hardware! I guess if you have a hammer, everything looks like a nail…

I shall certainly take the cover off (when it’s not raining) and check the tape heaters. They can’t be on all the time because sometimes the pump has the minimum 17W drain when the pump etc is off.

You certainly have got good correlation between R1T/R2T/R4T - very impressive, and probably within the spec of 3% resistance tolerance in the manual.

Thanks @squarepeg77!

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Yes, I’ve always seen a standby power of around 24W, and still do.
It seems to me that the tape heaters were only active when the circulation pump was running.

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Some ‘new’ behaviour from my heat pump is visible overnight, where the temperature gradually dropped towards freezing:


24W standby, with 66W when circulation pump is running at 60% is normal for my system after the engineer visit fixed the tape heaters.

At 3:34am the power goes up to 88W without the circulation pump - presumably some heaters kicking in below some temperature threshold.