Daikin Altherma sub-optimal performance

Hi All
I signed up to the open energy monitoring recently, after being of the electrification from heat trial with OVO energy for the last couple of years. With thanks to Glyn I have been able to utilise most of the monitoring kit used, just changing over the data logger. I can now finally see the full data from my heat pump, rather than taking daily readings. The experience of the trial has been challenging but that’s a story for another time.

Now I can see the data from my system it appears that the standby current is pretty significant. 60w typically vs 10-40w on other people’s systems. It does move around from a nice 23w occasionally to 60w most of the time but there doesn’t seem to be a pattern to the change. Does anyone have any ideas what might be causing this?

For the previous few weeks, when heating hasn’t been running, it would make quite a difference to daily electricity usage,~1kw is being wasted just in standby mode. I appreciate over winter it’ll be in standby mode less but the heat pump is over-sized so I think quite a bit of energy will be wasted over the course of a year.

System is an Altherma 11kw monobloc (EDLQ011CV3).

Any ideas to look at would be appreciated.

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Hello @HydroSam

Looking at a few other systems.

There are quite few systems https://heatpumpmonitor.org/#daikin

Do you have a low loss header and any secondary pumps on your system that might be coming on when the unit should be on standby? Could anything else be plugged in to the heat pump supply, that’s drawing at those random times?

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In the data book there are two figures that are similar to your data.

There’s a part that goes on and off, at random times/temp, the only way to know exactly is to trace this 33W difference.

EB-DLQ011-016CV3_CW1-EKCB-CV3-EK2CB-CV3-EKMBUHC3V3-EKMBUHC9W1_EEDEN18_Data-books_English.pdf (7.9 MB)


@TrystanLea no low loss header or secondary pump.

Vinny might be on to something. Originally the system had a 50ltr volumizer installed, this was removed by the second installer and replaced with an inline backup heater, since then PHE temperature appears on the information list, maybe coincidence, typically displaying a similar temperature to the leaving water temperature at the heat pump, I assumed this is something to do with the backup heater but it might not be.

I have switched off the back up heater at the supply spur as it’s not needed, and is basically a glorified inline immersion heater should the heat pump not be able to supply the full heating demand, it wasn’t required in -9C last winter so I switched it off (after advise on another forum). However the sensors inside might still be active as per the internal pipe heaters on the data sheet above, and the backup heater is still enabled in the main settings.

The backup heater is inside the house. I thought the plate heater exchanger was part of the monobloc outside but maybe not. But I’m not a heat pump engineer and whilst I understand the principles and have worked out most of the settings on this system I’m far from being an expert. My knowledge was built up off the back of an absent installer.

I could remove the backup heater in the settings menu and see whether that improves things?

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I had the same problem with my Atlantic Alfea. Are you using electricity meter for measuring electric consuption or magnetic clamps over the cables connected to yor logger?

It’s an Eastron electricity meter

My Daikin 9kW Altherma 3 has a consistent draw of 23 watts when not in use.

It does not vary by more than +/- 1 watt.

I have an OpenEnergyMonitor system fitted.

My heat pump was installed by Octopus Energy in June 2023.


Thanks all for your comments. I’ve not been able to track down what’s going on. I’ll mention it to Daikin if they turn up to do the service, it was due in July but no sign of them yet.
Heating season now so I’ll be looking to optimize that first. There appears to be lots of cycling going on.

Just to add a few details about my system, Mine is the older R410a Atherma monobloc. Just in case anyone pops over here from the reply I posted on the other Daikin thread.

What has been discussed over on the Octopus Daikin thread is similar to the journey I’ve been on over the last 2 1/2 years, just with others contributing to observations and conclusions they have been able to reach a similar point much faster. I was one of the participants in the OVO/BEIS electrification of heat trial. My first installer was eventually kicked off the scheme (and MCS), my system was then nursed back to health by another installer who was parachuted in, but they only had scope to improve some of the pipework and not provide any long term support.

Over this time for heating, I have removed the fixed-flow rate (at 50C!), tried pure weather compensation (house gets too hot even when set really low), low LWT with the Daikin controller modulation, higher LWT with Daikin controller modulating. I seem to be settling on a min LWT of 35C at 13C (generally the temp the house needs heating) and a max of 40C at -5C outside. The house was warm enough during the -8C we had last winter, with the heat pump gently ticking over outputting 5kw all day (another sign the pump is over-sized).

I think the heat pump is over-sized for my house, the radiators are probably too small in the kid bedrooms, they only lose a degree or two unless the lockshield is almost fully shut. The radiators need further balancing still, I end up with most almost fully closed to achieve a 5CdT. I think my pipework is less than ideal, there are several branches and plastic has been used in places, however with a low heat requirement I should be able to make it work. ‘Cheap’ city plumbing TRV and locksheilds were used and I am really struggling to balance the system, if anyone has a recommendation for improving the radiator valves please share. Only one TRV in my bedroom is actually used, so I don’t really need TRV’s.


To add a little more.
My original heat loss assessment was 8.5kw at -2.2C, then dropped to 7.8kw with the second installer. I worked it out as 4.5kw based on actual data once I’d understood what all this was about. If you want to read the detail I posted over on OVO’s forum here when I was part of their heat pump trial.

It seems like I have a very similar situation with over sized heat pump to @matt-drummer with a Daikin unit that can’t modulate down to where it needs to for my house.

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Hi Sam,

I truly don’t understand how these heat loss calculators are derived.

I guess they come from the same stable as the EPC surveyors!

It makes perfect sense to me that the best assessment of heat loss comes from past energy usage.

But their computer says `no’!

Unfortunately for me and maybe you it is a bit of a problem.

I don’t know what it is all about, I suspect covering their backs so we don’t end up with a heat pump that can’t provide enough heat when it is cold.

I think they should have more faith in their products and do it properly, oversized heat pumps don’t fit well with the philosophy of energy efficiency.

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At what air change per hour was the heat loss done(the one that decided the big HP)?
A clue might be in there, an assumed 1.5 ACH(leaky) vs a real 0.5 ACH(not so leaky) can have a 25% difference in the total heat loss value.

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Hi Vinny,

Theory is great but reality and facts are better.

I have lived in this house for two years and we always had it heated to 21c down to about 18c overnight, exactly what I want from a heat hump.

My heat requirement does not vary whether I have a gas boiler, oil boiler or heat pump, I am sure we can all accept it is the same.

The coldest day I have seen here was last December and it was about -5c all day.

That day was the most gas I have ever used here, 110 kWh. Some of that went on hot water and some was lost in inefficiency of the boiler.

Lets say I used 96 kWh on heating in a 24 hour period. My heat loss was 4 kW an hour on the worst day we have seen.

I don’t need a heat pump that puts out a minimum of 4.60 kWh.

How leaky my house is, what it is made of and how many windows it has are irrelevant if the calculation software is flawed. How can anybody work out the heat change per hour? Why would you need to when you already know the energy consumption of the house.

We know my heat loss as we know the actual heat lost in a day. It is determined by how much heat I needed to maintain the house at the same temperature over a 24 hour period.

Putting my heat loss at 7.3kW at -2c/21c is a grave error and one that I am now paying for as I was foolish enough to believe that the heat pump would just put out less heat if I needed less.

I never realised the minimum was so high in relation to the maximum.


Hi Vinny

I have no idea tbh. The paperwork doesn’t give any clue to this, but both installers had errors that weren’t picked up. I wasn’t provided the paperwork by the trial I was on until a year later, so had no possibility to give feedback.
The first calculation had the fabric of the building wrong, they’d made assumptions without asking the home owner, it was deep in Covid times to be a little fair, but they could have had a call to discuss, I wasn’t given this option, I was treated as a someone who wouldn’t understand, and at the time maybe I didn’t know much. The second calculation, whilst slightly better was still way out. With what I know now, a look back at historic gas bills over coldest days would have provided a better assessment.

It is what it is now, and I have to live with it as the installer has long gone AWOL, so unless I find some money down the back of the sofa, I need to find the best setup for the pump I have. I have been round lots of options, it’s now ‘ok’ with a SCOP of 3 but I’m not near the manufacturers quoted figures and I’m close to the bottom of the heat pump monitor list (albeit with just 6 weeks of data). Surely I can do better with a bit of tweaking, or I just have to suck it up and live with being ‘sold’ an over-sized pump.

I hope this doesn’t come across confrontational, it’s not meant to be, it’s just been a very long journey with this heat pump, it’s definitely better these days than it was to start with.


Hi. My heat pump installation is quite the same. I ve installed 8kW heatpumpon radiators, but my actual heatloss is 4kW. For now the most efficient way of running the heat pump is this - I set weather compensation to 40 degrees at 12 outside nad 45 degrees at -10. Its quite cold sometimes in Bulgaria. And here is the little trick to cope with oversized heatpump - I use the parameter “Compressor off time min” to reduce running time of heatpump. I set it to 30mins. This time is enough for the water in the radiators to cool down from 40 to 30 degrees. When the HP starts again it heats from 30 to 40 degrees so this makes 35 degrees mean temperature for the whole period - off and on time. This way radiators run alot more efficient and na cop of HP is better. The HP has also alot less starts and stops. Here you can see my monitoring - Emoncms - app view. As long as standby consumption i guess its some kind of heater - some installers put heater in condensation pipe to avoid water freezing. There are DIP switches that start and stop additional heaters.


@Ivailo_Stefanov - Where is the compressor off time min?
I don’t have that option in the installer settings and I haven’t been able to find a list defining the overview settings/field settings for my pump (EDLQ011)

Here’s a great article that explains how to calculate the heat loss of a house using whatever heating system is installed:


Hi Tim,

I read the article. It is interesting about other heat sources in the house. If you were just looking at pure heat loss then those other sources of heat are relevant but when working out the heat required to be provided by a heating source then they are not as those other sources of heat are always there.

In my case, I could add about 17kWh to my daily heat loss.

My heating provided 48kWh yesterday and the delta t was 12.8c. My heat loss was either 2kW or 2.71kW (if I added 17kWh to the heat going into the house).

Extrapolating both of those to a delta t of 23 (21c indoors and -2c outdoors) I get heat losses of 3.6kW and 4.9kW.

That is still nowhere near the 7.3kW that Octopus `calculated’ for our house. Assuming none of us were home and no electrical items were on the heat loss they calculated is still 50% more than that theoretical value and it is more than double the actual heat loss.

A poor job however you look at it.

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Hi @ColinS can you talk me through the reheat settings on the Daikin please?
Thought I’d bring it over on this thread to avoid confusion with the other chat about the optimum LWT for central heating.

A remind of mine. It’s now in reheat to 45C for DHW but it’s using the immersion to heat the water for some reason.


Sam , I’ve just put a detailed response on this on the ‘thank you…’ thread. Hope that helps. I’m new to this posting system so do not understand all the nuances yet. It might be best to have separate thread on Daikin - DHW optimisation - but have not worked out how to do that yet. If you can could you add my post to it as I seem to have reached my newbie reply limit on the other forum?

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