Ecodan Eco Mode for DHW versus Force

I know we were chatting about whether the “Force” mode for DHW on the Ecodan was making it less efficient. I can’t for the life of me find it amongst the threads this evening. There is so much wonderful conversation going on. So I’m giving up and posting a new thread, sorry.

Here is my system running yesterday where it forced the DHW on because I had DHW set to prohibited on the FTC5.

I’ve re-programmed my system today to allow hot water whenever the tank temp is 15 °C below the desired temp. Then I just push the desired temp to 10 °C so that the DHW doesn’t come on until I want it. At that point I push the DHW desired temp up to say 40 °C and it begins heating the water. So basically it’s still just an on/off switch for DHW but I’ve stopped using the force mode to achieve it. Here are the results from this evening:

So in practical terms the behaviour was the same.

I’m going to leave it using this new algorithm and see if there are scenarios where the outcome is interesting. I should probably fix that little on/off flip at 20:54 though.

1 Like
1 Like

I’ve not had chance to play with this myself, but one thought I had is that the FTC might override “Eco” mode if the heating system is calling for heat at the same time. Just a guessing.

1 Like

Yep, that’s possible. We won’t find out in about 15 minutes because my “cheap overnight” hot water run isn’t going to kick in because the water is already hot. I’ll keep an eye out for it happening.

As you know already, in the controller it does talk about limiting a long-running DHW so I’m hoping that the team who decided to implement that option considered what you are talking about. Of course they might have decided “heating was on, get the DHW done ASAP” as you propose.

1 Like

And of course @Timbones comes to the rescue, thanks Tim.

1 Like

I have to report a user complaint. Mostly because they don’t happen very often.

Apparently the shower wasn’t hot enough this morning. That’s because I had stopped doing my “force it on during the night” run. The bottom of the tank had dropped to 31 °C by noon.

I was just pondering altering my scheduling logic to allow independent schedules for heating and water so it looks like I shall have to implement that!

For reference, we can see that when I was forcing it on during the cheap overnight electricity window the tank was still at 45 °C for a late-morning shower.

1 Like

Here’s my first run with the behaviour Tim was after, there was no call for space heating.

This is re-heating the tank after a single shower.

As usual, it took about 20 minutes.

The max power was 3.5kW rather than 5kW when using the force.

The max flow temperature was 48 °C rather than 55 °C. The tank only got up to 38.5 °C rather than the target of 40 °C.

Note that (due to physics) we need the return to be at least the target temperature. Then there’s a 5 °C dt to add on top so the max flow temp needed to be something like 45 °C.

So, anecdotally it was more efficient, but only improved from a CoP of 2.5 to 2.8. I know every little helps, but this is pretty marginal.

I’ll keep running in not-force mode to see what happens.

1 Like

Any conclusions so far? I’ve just reconfigured my system to do the same experiment.

Yes, but I’d like to run for a few more weeks.

So far space heating has been markedly better, but DHW hasn’t.

Would be interested in what settings you are using? Watching this thread to see if I can steal shamelessly:)

OK, back at a computer now :slight_smile:

Slowing the flow in my system from 5 to 3 in the FTC5 seems to have made things better. Slowing it to 1 caused it to cycle dramatically because it couldn’t get rid of the heat.

As you can see, this has only been changed whilst it’s warm (early March) so it’s not clear if this slower flow will make things better all year round.

slow-flow is the one at the top above all the others:

The pump has been running a smidge longer which isn’t surprising:

Along with a slower flow I’ve also disabled Force mode on the hot water. Now I flip down to 10 °C to stop it running and flip it higher to get it back on. However, I set it to go up to 50 °C too often and so it worked too hard sometimes. Here’s an example from today where pushing it on to 50 °C (because we had loads of solar) was a bad idea for efficiency - specifically you can see it was reasonable when it popped up from 10 °C to 40 °C (but even that was only 285% efficient):

Anecdotally, it’s not been more efficient running it without Force. The data shows the same thing. I have seen some occasional wonderful runs, but on average it’s pretty much the same as before. I do see it taking a bit longer, and sometimes a lot longer to get warm.

"CanSetForcedHotWater": true,
"EcoHotWater": true,
"ForcedHotWaterMode": false,

Here’s the outcome so far, it’s better than the device doing it’s “heat up when the water drops 15 °C” but not much better. The other confounding factor is the new situation of people taking showers at 22:00 so even if the day was warm the water-heating cycle will be when it’s cold. The x-axis is the average temperature for the day.

Now I’ve dropped the temp to 10 °C to mean “off” it has of course had a dramatic effect on the average target temperature:

In conclusion, I don’t think removing Force has made a dramatic difference for me. However, I’ve got it coded and it’s happy flip-flopping between 10 °C and something else so I’ll leave it doing that and see what happens.

1 Like

I’ve gone for a slightly different approach - I’ve set a schedule so that DHW is prohibited all day except between 1pm and 2pm. As a result, the cylinder is heated up once a day, unless I have excess solar in the morning when the DHW is forced to run earlier (possibly to a higher temperature). Less flexible than fiddling with target temp, but I think it will work well for me.

I figure that efficiency doesn’t matter when there’s excess of free power, and putting it into the heat pump will store more heat than an immersion element would.

I’m mainly interested in running the DHW as slowly as possible, using the minimum amount of power (watts). Hoping that ECO mode will do that, though I’ve also got “Quiet Mode” enabled (an FTC6 feature with little to no documentation) so it might be hard to see a difference.

Here’s a typical cycle from yesterday, before I applied the settings described above:
(power axis lies - 3 kW is actually 2.6 kW)



(cycle stopped prematurely because DHW was set with a maximum duration of 45 minutes)


You lucky thing, we use too much hot water to pull that off, even with the 300 L tank.

I just had a user complaint because the water wasn’t hot enough.

Chasing efficiency can go too far.

I’m going to enable the overnight boost again.

I love being able to run my algorithm and choosing the calculation moment so I can see how it would behave :slight_smile:

bash --calculation-moment=2023-05-01T03:26:10

DEBUG: The power is off but will be more expensive in 60 minutes time and the tank is at 24.0 so aiming for a target of 54.0 °C to warm up water using cheaper electric

DEBUG: Turning on so we can heat the water (Power → true from ManageSpaceHeatingPower.manage)

DEBUG: We’re going to heat the tank to 54.0 °C because it’s at 24.0 °C which is lower than the trigger temperature of 39.0 °C and the flow is at 21.5 °C (SetTankWaterTemperature → 54.0 from ManageSpaceHeatingPower.manage)

Here’s something more tangible.

Effective outdoor temperature (approx): 15.0 °C

12:00 - 12:15
Forced (due to user complaint)
kWh: 0.9 => 2.1
CoP: 237%
Initial: 30 °C
Target: 38 °C
Achieved: 41 °C

12:50 - 13:15
Computer-initiated because the tank was cold
kWh: 1.2 => 4.1
CoP: 328%
Initial: 20 °C
Target: 38 °C
Achieved: 38.5 °C

13:35 - 14:00
Computer-initiated because solar was producing so much
kWh: 1.4 => 3.2
CoP: 221%
Initial: 38.5 °C
Target: 55 °C
Achieved: 50 °C

Conclusion: Heating gently from colder temperatures can give better CoP.
Conclusion: Heating to a lower target can give better CoP.

This is not news.

User comfort is still an important goal, if it wasn’t we wouldn’t need the heat pump.


I’ve had our home Ecodan 8.5kW running now for just over a week (Yey) and have been experimenting with the DHW and came across this thread.

We are on Octopus Flux and will have a solar diverter so my initial plan was to use the FTC6 to only turn on hot water during the night time off peak period. Any solar diversion to the tank would reduce the amount the heat pump would need to do the next night.

Unfortunately certain other members of the family take showers that are too long so some days it would appear the tank isn’t quite enough to see us through the day.

Another thing I discovered was that when the temperature probe is at the bottom of our tank as soon as one shower is had the temp has dropped significantly so if DHW is continuously on it would trigger with every use. I have tried moving the probe to the top of the tank and it only drops significantly in temperature when the tank is nearly depleted.

Therefore my next plan was to keep the temp probe at the top of the tank with DHW always on so the heat pump would kick into action if hot water was nearly depleted as a backup but have a 2am cron job to run a pymelcloud script to trigger Forced Hot Water.

However reading this thread I’m not sure it would be very efficient to do this.

So can someone think of a fairly simple way to achieve what I’m after and still be efficient, that is to have a main hot water run scheduled during cheap electricity at night but the back up of having an extra run if it looks like we are going to run out?

1 Like

I’m fortunate to have a thermal store heated by solar thermal and PV so DHW isn’t an issue for a significant portion of the year, especially now the three children have more or less gone for good, but over the Winter months I heated the AHSP DHW using my Eddi diverter on a scheduled basis to match my Octopus Go tariff rather than have the Ecodan ASHP start up.

Heating DHW isn’t terribly efficient in terms of COP and I figured using cheap rate electricity would be better (although I stand to be corrected!).

As with Nick, I suggest it’s best not to worry too much about this. The gains I’ve made have been marginal and the peace-of-mind that comes with avoiding all the “is there enough hot water” angst means it’s generally best to just get on with.

For example, a couple of days ago we had a power cut so the cronjob didn’t run and the server didn’t come back up so it didn’t even get anacron’d. As a result the water was cold and my beloved wasn’t impressed.

There was also a lot of chaos last night when we wanted three showers in an hour and the system was trying to hold off until it was more efficient. We turned it on with MELCloud and my server turned it back off! Fortunately the second time we turned it on the “oh someone forced this on” code kicked in and left it alone.

Wouldn’t it be better still to run the heatpump during the cheap rate? Even if it only gets a COP of 2, that’s still twice the heat into the tank compared to direct heating. I don’t have solar divert, I just put excess electricity into the heatpump to heat the water until the immersion takes over. (~54°)

There’s the trade-off between having enough hot water for the entire household vs. spending as little as possible to heat that water. You’ll get more complaints about the former.

Your plan above is probably good enough for what you need, and efficiency will probably be fine. Remember: DHW is just 1 tenth of your annual heat demand, so there’s limited value in hyper optimising it.

Heating the water to a higher temperature during the cheap rate, storing more energy in the tank, might allow for longer running showers. Less efficient, but that’s less of a concern while electricity is cheap.

The FTC has a setting for how much of a drop in tank temperature before it will turn on again. You might want to try increasing this to 15° or more. You can also prohibit the hot water during certain hours, e.g. just before cheap period and during peak period.

1 Like