WD Curve scheduling Daikin Altherma

Sorry if this is in the wrong area or if already asked - I searched forums but couldn’t find anything.

I am a new user of a Daikin Altherma 3 ASHP (EPRA18DV3 with ETBH16D6V hydrobox), hot water all great, heating is going well but I’m pretty sure I’m not getting the most out of it.

I’m currently using wall thermostats to trigger heating but with the (adjustable from 0.5 - 3c) fallback on the stats I’m a bit concerned the system is being triggered more regularly than is ideal.

I’ve been told some models (Vaillant) are able to have heating schedules so the weather curve controls when and how hard the pump is running at different times of the day. My curve is set so that the water temp is adjusted but it is only triggered when the wall stat tells it to deliver heat. Also I’m not sure why the pump controlling these temps any times would be any different in terms of the pump switching on and off than a wall stat controlling them.

One of the installation guys (who I think had a vaillant) said he only uses the curve but I didn’t think to ask at the time how this is managed.

So, I guess a couple of questions.

  1. Is my current set up ok? Is the repeated powering up and down over a 0.5c temp difference going to adversely affect my compressor over time?
  2. Is it possible to run the Daikin solely off the WD curve? And if so, what to do if, say, solar gain means rooms are roasting? Would the pump still run based on the weather curve? Presumably the bathroom rads (which don’t have TRVs) would still demand heat?

As you can tell I’m not 100% on top of this stuff but v keen to learn quickly.



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Hi @Hammerd2,

Do you have all TRVs on max (this is called open flow around here and in the industry) apart from maybe a couple bedrooms? This assumes they balanced your radiators however and they are sized for the heat loss along the room.

Do you know what flow temperature your system is running at? It sound like it may have been setup as fixed temperature.

Do you know the heat loss at design temperature (eg -3C) for your property?

Daikins can (generally but don’t know about yours specifically) run in pure weather compensation mode (called leaving water temperature on Daikin controller FYI)

What is the wall stat? Hopefully it’s the Daikin Modoka :crossed_fingers:t2: as 3rd party stats are known to be problematic.

Can you go into the menu and let us know the input (electrical) and produced (heat) energy values for hot water and space heating separately?

See here for example. Assume you have the same controller fitted somewhere?

TRVs should be used to control solar gain for example on that point - so needs to be an exception to the first line at top of this post.

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Hi Stephen, thanks so much for replying, really appreciate it.

Ok, here goes!

TRVs are (except for a few rooms - bedroom, couple of small store rooms) all set to max.

The system is set to follow the weather dependent slope offset curve so is 55 at -3c outside.

The design document has the building heat loss as 11.73kw (is this what you meant?).

Modoka was initially quoted but there was some last minute problem so I have Heatmiser NeoStat v2 wall stats which integrated fine and are app controllable.

Since late august we have :
Heating produced 1,314kwh, input 340kwh
Hot water produced 483kwh, input 143kwh

My setup is slightly complicated in that I’m on a V2H trial with a relatively small EV battery (Leaf 24kw), so I’m currently charging that & doing hot water and a house preheat between 00:30 & 04:30 (Octopus Go) then trying to maintain as much of the EV charge as possible for daytime/evening heating runs. I have ~ 13-14kwh of ‘cheap’ 9p electricity to feed in from the car which is permanently connected.

So I have a combined need of using as little 30p electricity as possible while reducing west and tear on the ASHP system/compressor hence my wondering if having it always on low and slow is better overall than it cycling every time the fallback level is hit (Heatmiser lets me change this from 0.5-3c range). But something needs to trigger the heating at some point and I can’t see how the west on the system is any less if it’s the ASHP itself or a wall stat isdeciding when it’s cycling.

Hope this tells you everything you need to know, please ask away if I’ve misunderstood anything.

Best regards



I’d say your best bet is to change the settings to pure weather compensation (leaving water control) as 3rd party stats are on/off and are not providing load compensation modulation data back.

Also, suggest the curve is too high at 55C/-3C

Try adjusting down until equilibrium is reached, (ie stat doesn’t change reported temperature, even dropping slightly- as otherwise you won’t find the closest curve)

One slight downside is that scheduling can only be done on the daikin controller once in leaving water control mode (pure weather compensation )

Start at say 40C flow at /-3C outside And ~30C at 16C

Yep :ok_hand:

That’s weather compensation (leaving water control) - it’s “on” all the time, but you can schedule (& manually adjust if needed) the offset to provide different indoor temperature at various times of the day

Thanks again.

So, the wall stat is connected to the ASHP, so should I just set that to always be on (say, 30c or something?

I can’t see anything in the set up screens on the wall unit to allow any scheduling of offset options - any idea what part of the menu it might be on?

It’s a very odd mind space to think that having it basically ‘on’ all the time will be more efficient/economic! Seems like it’ll be using a decent chunk of power (when it kicks ive noted it can draw anything from 1.8-4.5kwh) all the time but happy to try it out if I can find the settings to do it.

I’ll have a dig around in the menus again and try going in to installer mode to see if that throws up any fresh choices (I’ve changed hysteresis (???) on the hot water settings in there) bit if you have any tips I’m all ears as I’ve only seen schedule options on the water menus.

Again, thanks for your help, good forums are full of so many helpful/knowledgeable people, this one seems like a good one!



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Sorry, Not quite sure what you mean by this/how to change it. The menus are showing I’m on WD mode already

Not at home, but under Installer profile (5678) select Main zone—>Control

Select leaving Water.

I’m not in front of the controller, so that’s from memory

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Probably as it’s racing to get the flow temperature very high- and then the stat turns it off.

Low and slow is best if possible

For comparison, my weather curve starts at 32C (16C outside) and ends at 42C-ish (@-3C outside)

It’s high at 16C due to minimum output constraints, which there is plenty to read about in other threads!

You can tell from the mobile app when in pure weather compensation (leaving water control) as there is now a manual flow temperature offset adjustment, and heating schedule ability is lost in the app (can only do schedules on the Daikin controller - and is flow temperature offset from the curve)

Great thanks.

I’ve found the setting so I’m giving it a go! Will report back on a couple of days when it’s had a chance to bed in.

Have a good weekend


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Yes I have this now on the app.

In the schedule then it offers the offset at various times so it’s +/- 10c from the temp on the slope right? So if I want it cooler overnight set 22:00-02:30 at, eg, -5, then +5 for getting warmer for waking up.

Is that about right?

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Spot on :ok_hand:t2:

Hi Stephen

Thanks again for your time over the weekend.

I’ve got a much better handle on how things do (& now, hopefully, will) work.

Now in a process of tweaking wall stat and hydrobox settings so I can get the most out of the system and get the comfort levels we’re after.

It seems that setting the wall stat high enough to almost always be demanding heat and the hydrobox settings not quite high enough to meet the temp demanded will mean an efficient use of the heat pump and a level of warmed water going through the radiators to maintain an equilibrium so that the evening sawtooth temp graph I’ve been getting is smoothed out as much as possible.

I think at the moment I’m about 0.5-1.0 c short of the sweet spot but have a route to get there.



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