I am lost and confused with my Daikin heat pump

As per the title!

I have asked for a fixed flow rate of 37c at a delta t of 5c.

Why doesn’t it just do it?

I’m struggling with this, it is so inconsistent, some days it is really good and then things happen, DHW is OK then terrible, heating after DHW seems to go wrong, it doesn’t seem to get up to the requested flow temperature.

If I leave it alone for hours it is OK, then I turn it off because the house is too hot and when it restarts it is terrible, it never picks up where it left off. Sometimes the initial heating cycle is good and it settles down quickly, other times not.

I haven’t been messing with anything other than bumping up the flow temperature to kick it into life as it seems to struggle at times to get to the requested flow temperature.

Does anybody have any ideas, is it me, the heat pump or something about my house?

Here, why doesn’t it just heat the water to 37c as I have asked it to?

@matt-drummer at the risk of opening old wounds :face_with_peeking_eye:, this could well be related to the now surely infamous Leaving Water before BUH R1T and Leaving Water after BUH R2T sensor discrepancy on Daikin Altherma A2W Heat Pumps with a backup heater?!

Hi Stephen,

I think you may have misunderstood something, no wounds here as this is not a conflict :slight_smile:

Honestly, I need to use the temperature of the water coming into and leaving the house to calculate heat produced if I want to know what is really going on, what anybody else does is entirely up to them.

Whatever various temperature sensors report in the heat pump my water coming into the my house is not what I have asked for and neither is the dT.

I don’t know why and I don’t know why some days are good in this respect and other days are bad.

I have always felt there was something amiss with my heat pump, there are clues, my DHW production varies massively and my LWT and heat production are erratic, it’s not consistent and it’s not smooth. The flow temperature rarely builds smoothly, it fluctuates up and down, it’s like a misfiring car.

It is not that my LWT is under the sensor at R1T or R2T that is my concern, I measure with a heat meter.

My concern is that the temperature doesn’t build smoothly and quite often it never even gets to what I have asked for.

Even if the temperature in the heat pump was wrong somewhere I would still expect it to be steady, I would expect the error to be constant.

Something doesn’t feel right with it, I don’t really care how well or how badly it was doing, I just wish it was consistent so I could work out was what wrong.

The app and my MMI are showing the same as my heat meter, the sensors in the heat pump are not the issue.

It must be my settings.

I have overshoot at 4, I know I can reduce it to 1 but can I remove it completely?

@matt-drummer my point I didn’t make clear enough is:

I think I’m seeing similar now I’m looking at a different sensor (closer in accuracy to your heat meter).

I’m seeing odd things like you are where it doesn’t try and reach the targetTflow, yet if I look at the previous sensor (R1T), that then indicates the unit is at or just over the target, whereas R2T is below it.

Maybe. That was all.

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Hi Stephen,

Yes, sorry and I understand.

I am at my wits end with this heat pump.

It has taken me three hours to get it running properly again after the DHW run at 13.00 today.

It was fine last night and this morning but I had the same problem yesterday after the DHW cycle.

It never started the heating cycle properly, it defrosts with no sign of ice and then I have to stop it and start it again to get it running like it was.

It’s driving me mad, I just want to get to a point where I can leave it alone confident that it will behave the same as it was earlier in a day.

I can’t seem to do that right now, I always seem to have to do something to get it to run properly.

I really wish I had something else!

My honest opinion, it’s a pile of junk.

So I upped the requested flow temperature to 38c at 17.15 to try and get the temperature I wanted of 37c and it is now falling! It is just doing whatever it wants, I seem to have no control of it.

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Does the heat pump have the ability to learn? Maybe @marko is best placed to answer this?

If it has, I’d venture the suggestion that by you (@matt-drummer) are changing so much so quickly, it doesn’t know whether it is is coming or going.

If not, fair enough, I’m barking up the wrong tree. If it has but we don’t know it, it’s something to consider.

Hi Robert,

I may have changed a lot in the last two months or so, maybe it does learn.

But I haven’t changed anything in the last two weeks other than flow temperatures and I have only done that when needed to prompt it into action.

I have left it alone really, pretty much.

I certainly can’t do anything with my DHW, I have changed nothing yet it is all over the place.

It was working fine yesterday morning and this morning but after the DHW cycle it is not happy to resume heating, I have changed nothing. All I do is turn it off and start again, and it is better.

I think I have a flow problem though, this DHW from a couple of weeks ago, 35 lpm

And today only 26 lpm

I think I have an issue somewhere.

Check your strainers if you think you have a flow problem - Do you Biocide and Inhibitor in your system?

Yes I use inhibitor but nothing else.

I cleaned the filter that is on the return to the heat pump a few weeks ago.

Are there any others, does anybody know, inside the heat pump?

I think it’s just the one on the return valve. My installer was quite insistent on using Biocide as well as Inhibitor on a low temp system - he showed me some pictures of a system without it and it was quite a mess after a short period.

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Hi @Stephen_Crown @matt-drummer

I’m very suspicious of the Daikin HP firmware and its use of the different R1T/R2T sensors for various purposes. I need to check, but I suspect that it uses different sensors for Flow dT calculation vs. Flow temp. Mad. But likely, given the ±BUH option and the HP vs MMI software. My use of a 4C overshoot for FlowTemp confuses things a bit, I might fiddle with that if I can be *rsed - too many more urgent things to do at Christmas time!

In the meantime, I haven’t heard anything back from my inquiry to Daikin. I did prod them yesterday but only got a “reassuring” message. I did take the opportunity of their customer service survey request to point out that answering my questions might improve my view of their service offering. :man_facepalming:

I don’t think so John.

The BUH equipped models need the LWT temperature sensor at R2T after the BUH as if the BUH is in use the LWT will be higher than it is coming out of the heat exchanger at R1T.

R2T measures the temperature of the water leaving the heat pump.

R1T measures the water temperature leaving the heat exchanger.

There is a temperature drop because the pipes and equipment are not insulated, the water is bound to cool down.

My app, MMI and heat meter all report the water coming into my house at the temperature recorded at R2T.

If there was less of a temperature drop between R1T and R2T that wouldn’t increase the temperature at R2T, it would reduce the temperature at R1T.

The heat pump is working to get the flow temperature requested as it leaves the heat pump, the last place that is measured and reported is R2T.

This is my understanding looking at pictures of the heat pump and the schematics.

Do you think something different is happening?

As long as the temperature of the water going into your house is that recorded at R2T and you use that in your heat calculation then everything is good in that respect.

If the temperature of the water entering your house isn’t that shown by R2T then what is it?

Two points:

  • I think we’re all agreed that R2T is the most sensible place to monitor outbound flow temp for BUH-equipped systems - no need to discuss that further
  • What the HP/MMI should use and what they actually use for various values from the sensors are quite different things; I might be barking up the wrong tree, but it’s a combination of very complex hardware/software, and as a software developer who has struggled with co-ordinating different teams and many cubic metres of intractable code, I am very cautious about assuming anything!

Onward! :grinning:


Hi John,

As far as I can see the MMI and the app report the value at R2T as LWT, do you agree?

The value of R1T is reported in the MMI and I see a value, like Stephen, that is about 1c higher than that reported at R2T, there is a reported temperature loss, whether that is true or not I don’t know but there’s lots of uninsulated pipework there. I think there is a loss.

I don’t know how the MMI calculates heat produced but none of us use that, it’s of no concern to me.

The temperature loss is though.

I worked out yesterday that the extra 1c or so at the heat exchanger costs around 150wh of electricity at a COP of 5, quite a lot of electricity to waste.

I think there is value in adding insulation and mine arrived today.

I am going to give it a go.

I too have contacted Daikin to arrange a visit to check my heat pump. I am convinced that something is not right.

  • LWT @ MMI/App = R2T, yup.

  • Various R1T/R2T differences reported, attributable to a) heat loss b) thermistor calibration/performance variation - agreed. I’m interested in finding out why mine seems so much greater than e.g Stephen’s; that extra 1.2C I experience constantly makes all the difference to heat output calculations at dTs around 5C

  • I don’t use the MMI’s calculations, but since they seem to correspond to my calculations using R1T, and not R2T, there is a distinct possibility that the MMI is using different sensors outputs for different calculations/displays, especially as the BUH is an option that requires sensor usage to be configured in the depths of the software

  • I’m really looking forward to your feedback from the new front opened in the war against unwarranted heat loss AKA insulating the BFPs in the HP case; details of insulation, ease of application and resulting dT is of great interest

  • It will be interesting to see if Daikin a) reply b) provide a date within the next 6 months!

Hi John,

I will keep it updated as you would expect :slight_smile:

But if we get R2T close to R1T you won’t see greater heat output, this is what I am trying to get across, what you will see is reduced electricity consumption, possibly anyway.

It is a subtle difference. I would not expect any insulation to increase the temperature at R2T, I expect it to reduce the temperature at R1T as with reduced or eliminated heat loss between R1T and R2T the compressor wont have to produce such a high temperature at R1T to achieve the requested LWT at R2T.

The only caveat I have is that at minimum electrical input even though the R1T temperature is lower it may not actually use any less electricity as it is already using the least it can.

Once I get to a certain level of electricity consumption it doesn’t matter how much I lower the flow temperature, it never uses any less electricity.

What we may be able to do is use a higher flow for no less electricity and generate more heat.

I am really curious now to see what affect insulation has.

Maybe there is a reason Daikin didn’t add it that is not related to cost?

I f you look at Stephen’s picture with the covers off you will see some insulation on some pipework, whether Octopus added that or it comes like that, I don’t know. I don’t know if mine has it, I wonder whether yours does, maybe that would explain the difference you are seeing between your data and Stephen’s?

I really need to set my monitoring up like yours and Stephens, I am sure we would all like to know what differences there are between the data direct from the heat pump and from a heat meter.

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@matt-drummer et voila:

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This is Daikin factory fitted, Octopus did not fit it for info.

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I really need to set my monitoring up like yours and Stephens, I am sure we would all like to know what differences there are between the data direct from the heat pump and from a heat meter.

I’m sure we’d all really appreciate that! Thanks in advance…

My only interest is in getting accurate data on the cheap :crazy_face: - I want to be able to make adjustments against a reasonable baseline. So getting to understand the sensors and software’s actual performance etc. is important, rather than absolute cost/efficiency/whatever.

Maybe there is a reason Daikin didn’t add it that is not related to cost?

Haha, you jest! It’s a big corporation… although there may be some other reason, I’m not sure what it would be - keeping parts warm in the winter?!

I think it unlikely that Octopus do anything besides install the units, unless they do that in the warehouse prior to sending it out, in which case they carefully wrap it up in the original packing and transport labels. They certainly didn’t on mine. The manual pictures look pretty much like Stephen’s.


Hi John,

i am an accountant, I understand that they will want to save money, they did this by building one heat pump and turning it down to make three `smaller’ ones!

However, they have fitted some insulation and for only a tiny extra cost they could have insulated the whole lot and get much better performance.

Either they are really stupid or there was a reason, I am not sure I can discount either option!

I’m not sure the data needs to be entirely accurate to make improvements to our own heat pumps in isolation, but it does need to be consistent and reliable for sure.

The last time I looked, which was weeks ago, my MMI reported similar electricity consumption to my meters but the heat production was lower than that reported by my heat meter.

I will try and check again later…

Just looked at my MMI, it’s not very easy to read but the energy used and heat produced look to be almost identical to my heat meter.

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