Improve efficiency: Turn the heat pump off

Huh, that’s interesting - that would explain why I’m not seeing a difference after turning off Eco mode while forcing the hot water on at the same time every day. I’ll try it the other way, see how it performs.

(I had turned off Eco mode during the colder months in the hope that it would heat up the cylinder quickly and get back to heating the house sooner)


I was just about to dive into this, but I can see a hiccup.

In my case I’m regularly heating up the hot water in the middle of the night. Recently I had started turning on the heat pump around that time and a subtle bug meant it would end up doing space heating before considering switching to hot water. As a result I was spending a lot of money heating up the house during the night for no reason.

I like Paul’s suggestion but I believe the Ecodan will simply turn on and blunder off doing space heating even if the desired tank temp is set high. I may be wrong.

Good news on the low temp though, I was able to send an update which put the SetTankWaterTemperature down to 10 °C so that would be the “off” setting you are after.

I’ll probably wait until the warmer months before trying Eco mode again, when it won’t be competing with space heating, and I’ll be looking to minimise peak power usage while the sun is shining.

I’ll share this with you for kicks.

We went away for a few days so I blocked the heating. We got down to 15 °C inside and then it took about seven hours for things to come back up again fighting against what was fairly cold outside.

Now if only we could cope with living at 15 °C we could save loads of money on heating.

From this chart I’d say that I can see how the space heating would run for a long time, but it is pretty rare for me that it runs so much of the time that we couldn’t sneak some DHW in. I suspect I’ll come to the same conclusion as you that in Eco mode the DHW doesn’t get the job done quickly enough. However, maybe I can lean on my estimate of when the heating needs to come back on (based on the temp dropping) and pair the up with my “should the DHW be on” to decide if I can let Eco mode do the job. If it decides that Eco mode isn’t getting the job done then it could force the DHW.

I keep thinking up reasons this won’t work and then working around them. It may actually work.

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Another update from me breaking my system and it dropping back to default mode. It was running continuously from 14:00-18:00 so that’s four one-hour bars in the chart.

Here it is in MELCloud just for a change:

So when running continuously it used 2+1.6+1.8+1.7 = 7.1kWh and produced 6.3+5.6+5.8+5.5=23.2 for a CoP of 3.27.

Now, compare this with yesterday. The weather was practically identical and the house was set up the same.

So yesterday, (when my code was turning it on-and-off) it used 0.6+1.1+1.1+1.2=4kWh and produced 2.2+4+3.9+4.1=14.2kWh for a CoP of 3.55.

Yes, the CoP was better by turning it on-and-off, but that’s not the interesting part of the story. It only used 56% of the energy so turning on-and-off reduced the bill from 2.41GBP to 1.36GBP.

Of course, I got less heat out too, but it turns out the house was 20-21 °C yesterday and 21-22 °C today with constant-running. I could have held it back with TRVs, but we’ve all got them wide-open these days so that didn’t happen.

From where I’m currently sat, changing to constant-running would increase my power consumption from 4kWh to 7kWh which is a 77% increase.

Having it modulate down further would help, but I was surprised how easy it was to consume so much more power just by having this change. I can see how people are getting into trouble, even if their CoP seems good. They could still be consuming lots of energy that isn’t really making a difference to their lives.

(on the bright side we did work out the largest sphere you could host in a tetrahedron so the distraction was worth it :slight_smile: )


Thanks @pault

I think your useful observation is getting lost in the on/off discussion. Ironically I was looking for your post and even posted something else to this thread this evening :slight_smile:

I’ve taken the “force DHW” off over here so it’s got it’s own place to flourish.

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That is some statement!

I’m not entirely clear which chart is which situation. Is the lower chart (less consumption) where you are forcing it back to default mode?

This again demonstrates the highly complex nature of controlling HPs that the average Joe has little chance of understanding or manipulating to their benefit.

That’s understandable, it wasn’t clear enough. I’ve edited it to make it clearer if someone else comes along.

The top chart is it the default behaviour of it running continuously from 14:00-18:00.

The bottom chart is where my code is handling when to turn it on-and-off.

Yep, that’s why I’m sharing what I’m doing so people building new control algorithms can use this data (well, anecdote really because it’s just one system). Also, Tim’s comparison website will also show the behaviour of highly tweaked systems so we can all discuss what works well for different use cases.


Agreed, but, as you say, it is more than just COP!

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I have been looking at something like this with my Samsung (but am a little way off actually doing anything).

I don’t have a heat meter, but do have heat pump flow/return temperatures and a pretty constant flow rate.

I was looking at the local My Heatpump app with the Carnot calculation switched on.
Then, drilling down into specific instances of the HP coming on; the Tado mostly calls for heat for 10-15 minutes but when a temperature increase is needed, it will be on for maybe 1.5-2 hours.

What I could see was, for the first n minutes, while the deltaT was increasing, it was a better CoP, then as deltaT starts to reduce (I guess all the water’s circulated at least once) the CoP also starts to reduce.

I’m doing some test on varying the pump speeds but when I’ve completed those I’m definitely going to see if I can automate switching it off when deltaT/the efficiency starts to drop.

The question then will be, how long to leave it off for to achieve the desired steady or increased temperature?


Yep, I’m doing something the other way round in that I’m keeping it on if dt > 5. Of course that means when dt drops the code will consider switching off which is the same effect you are after.

You can also see the code taking things gently by not turning off until the dwell time has passed.

I’m doing a similar dwell to bring it back on.

I’m waiting until “the radiators” have become “cold”. Of course “cold” depends on the season. Also, I don’t actually have a reading from the radiators so I’m using the return temp as proxy. It works surprisingly well.

Basically, if the radiators become cold it makes the people feel like the room is cold so my heat pump spends its life trying to keep the radiators between something like 26 °C and 40 °C.

You’ll want to be consider the house temperature too, and keep it running if it’s too cold, and only attempt to optimise COP when warm enough. Otherwise you’ll get complaints…

I wait for the compressor to turn off naturally, and then I keep it off for ten minutes before allowing it to turn back on (if it wants to). See this thread for more on turning of heat pump between cycles:

I know what I’m about to say sounds ridiculous:

I don’t take the house / room temperature into consideration.

My old oil boiler from the 1980’s just used the return temperature as it’s guide. When that got high it stopped heating. Stupidly simplistic.

I was somewhat surprised to see this mechanism worked with the heat pump too.

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Fairy nuff. Do you need to keep the pumps running so you can measure the rad temps at the return sensor? Or do you find the sensor point loses heat at the same rate while the water is stationary?

I’ve heard that Ecodan’s auto-adapt feature keeps the pumps running for this purpose.

Again, I’m going to say something ridiculous:

The pumps are too noisy.

Clearly they aren’t really, but it’s so quiet where we live you can actually hear the glycol moving around and about 2% of the time it’s distracting.

It turns out there’s no real benefit to pumping the water around if it’s not getting heated, we may as well just let it settle and slowly warm up the place it’s in. The radiators in our house are a bit like having a big warm dog in the room. We’re treating the volume of the radiators like a buffer tank, the heat pump pushes water into them and then it heats up the building. We’re pretty open-plan so we can get away with it because we don’t get one room being very different from the others.

I’m surprised it doesn’t affect the comfort much. I suspect it’s because we turn the heat off pretty quickly so it doesn’t have time to overwhelm the room. I’ve certainly noticed that when it’s running continuously the rooms get oppressively hot.

I did some ad-hoc experimentation where I measured the radiator temps dropping and it was close enough to the fixed “return temp” sensor that I felt OK using it as a proxy.

Anecdotally I have a radiator about 300mm from my chair in my office. I lie my arm on it to warm up. When I find myself thinking “ooh, that’s getting a bit too chilly” I go to nudge the heat pump only to find that the algorithm has just turned it on or was about to in the next couple of minutes.

I believe that it’s all down to the magic numbers in the code which makes me sad. I want it to be more robust so it handles disruptions better.


You’re not wrong. Our “plant room” is the old airing cupboard at the top of the stairs, so the noise of pumps carries around the house. I had the installers reduce primary pump speed down to 3 because of the noise, which helps. I certainly wouldn’t want them running all the time when not needed.

My return sensor seems to cool down slower than the rest of the system, hence why I’ve gone for a fixed 10 minute pause between cycles.

Slightly off topic: Today I discovered a setting on the Ecodan called “Quiet Mode”, but there’s precious little information about it online. I think it’s limits the maximum power it will go up to, which might be worth playing with instead of trying to control flow temps. Can be set to a schedule, or all the time.


It turns out the opposite seems to be true for me! Probably because some of the radiator pipework is insulated outside the living areas. So, the auto adapt mode is beating my best algorithm (cop about 4 vs 3.6) because it can run the circulation pump without the heat pump for 20-40 minutes a go, which I don’t think I can over melcloud.

The smart control now only decides when to reduce setback, provides remote control and feeds emoncms.


BTW the FTC5 does not have the “Heat Pump Settings” entry in the service menu.

I followed this guide and it’s not in there.

BTW there’s a nice person called “mjr” over in those forums :slight_smile:


That is literally one of the two references I managed to find (the other also on same forum), but it doesn’t explain what the 3 available levels do. Maybe I’ll just have to try it out and see for myself…
(it’s an FTC6 feature).


It’s in Service not Initial Settings on mine. It’s definitely there for me. It’s also shown in the instruction manual. I’m pretty sure mine is an FTC5.

However, I’m still not entirely sure what the underexplained settings do in practice!

I don’t remember whether “Quiet mode” is among them on the FTC5.

Him? He’s a damned nuisance because he keeps popping up in my search results when I’m trying to figure out how these heat pumps work!