Daikin Altherma hot water priority

I hope this is a suitable forum for my question.

I am having trouble getting my Daikin Altherma EDLA09DA3V3 to heat hot water whenever space heating is active.

I have the hot water set to “schedule only” (no reheat) and the schedule is for 1pm-2pm. The tank is well below the target temperature (45C), but the heat pump continues with space heating.

Is there some trick I’ve missed?

This wasn’t a problem when we had solar surplus as we have an Eddi which keeps the tank temperature topped up nicely. But I haven’t seen a solar surplus for a while now :joy:

I have just activated “Powerful” hot water mode and watched the valve change to the hot water position, so that works. It just seems that space heating has priority when I would have expected hot water to be prioritised.

I have been making do with boost heating via the Eddi, but would like >100% efficiency. (On a side note, Octopus only connected the Eddi to the immersion heater AFAIK…)

I have looked through the manual and installer reference but not found anything about hot water priority, apart from quite confusing sections about backup heaters etc.

I suspect I have to adjust heating and/or hot water schedules, but thought I’d ask here before I make any more changes.


I think this might not have got the attention of some of the more knowledgeable people on heat pumps because it’s missing the heat pump tag. Are you able to add it as the original post creator?

I’ll try and start things off but hopefully others will come along and help if you haven’t solved this.

Firstly is this a new thing that’s started over the recently cold snap? There is a setting which prioritises heating over hot water below a certain outside temperature, and will then only allow DHW heating via the immersion.

If this isn’t the case and the issue has been around a while, then we will need to dig deeper.

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Thanks for noticing the thread, I’ve added the heat pump tag.

I think it might have been user error, where I didn’t enable the hot water schedule after setting it, or I had the set point too low.

I set a new “comfort” hot water interval for 9pm last night and it interrupted the space heating. It did the same in the 1pm slot today, so looks like we are good.

Are there situations where space heating takes priority over hot water?

Edit: my immersion heater is only connected to the Eddi, so the heat pump can’t control it.

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If you want to configure this on a Daikin it is possible to have the ASHP control the Eddi with the use of the add on relay board.

You can also use this to run the heat pump to heat the hot water and house at a much higher efficiency, it requires a couple of cables and a few settings but is explained in the myenergy and Daikin installer guides.

Glad to hear the hot water is working, What sort of COP are you seeing for the DHW cycle?

I don’t have a good way of measuring the COP yet. My Daikin MMI displays useless values - 0 or 1kWh per day for electricity. The “heat produced” might be more reliable - it looks plausible.

I have added a CT for the entire heat pump feed which is connected to my Eddi, and have the heat pump power available in Home Assistant.

I’ve just received an M5StickC, so will try and get that setup with ESPAltherma, with a view to pushing the data up to heatpumpmonitor. I might need some help from @Stephen_Crown :slight_smile:

I have a relay board in the Eddi, so might look at getting the heat pump connected to it, although I don’t think Octopus ran the wiring for that. They nearly drove off with the contactor / relay…

If I get ESPAltherma running and connected to Home Assistant then, I could probably setup some automations for hot water top-ups etc.

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@squarepeg77 let me know what if any help you need.

Lots of trial and error on my part getting the end to end working! Well worth it however.

Make sure you have strong WiFi very close to the stick. Being inside the heat pump outside unit doesn’t help with signal strength!

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@Stephen_Crown I’ve got the M5StickC flashed, connected to WiFi and talking to Home Assistant via MQTT. I haven’t connected it to the heat pump yet.

What sort of WiFi signal strength do you think is viable? My heat pump is about 5m from my house and 12m from my primary router. I have a WiFi repeater I could setup.


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Hi @squarepeg77

-67dbm seems to just reliably - just (Any lower - negative figure - and it starts dropping out, and very quickly stops connecting altogether)

I added a Google WiFi puck literally on the other side of the wall from the heat pump (i.e. inside), and placement within half metre made the difference between stable and dropouts.

I got no connection at all until I placed WiFi mesh puck very close.

What are you getting now inside the house?

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Hmm, I just took the M5StickC outside and put it next to the heat pump, and was getting -81dB to the repeater plugged into the nearest socket :frowning:

This could be a challenge.

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Try it first - you might be ok, it may be noise from nearby WiFi from other houses that hurts signal.

You’ve got nothing to lose!

Yes, I’ll report back once I’ve got it wired up.

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Just about to start the ESPAltherma with HA also, I am a little disappointed with the Daikin Stats from the API and display… just waiting for the post person :-), I have a CT clamp on the Heat Pump and GitHub - speleolontra/daikin_residential_altherma: Home Assistant Integration specific for BRP069A78 Heat Pump Model, via Daikin App Onecta. Users have good experience also for BRP069A62 and BRP069A61 (but not tested directly). integration from HACS.

Is there a guide @Stephen_Crown from this community to integrate to Open Energy I can follow? otherwise, I will trawl the GitHub, cheers Neil

Not all in one place to be honest - sorry about that.

I’ve noted bits and pieces here and there in threads on this forum, and have sent some files/info to @matt-drummer separately via the message function.

Where have you got to?

Sorry to hijack a thread, very early…just waiting for the M5Stack M5StickC PLUS ESP32-PICO Mini IoT Development to arrive in the post

No worries. But maybe we should have a new thread specifically to discuss ESPAltherma?