Hi Tim,
I am no expert either, so it could be.
Octopus fit an automatic bypass valve.
I have this completely shut.
Maybe it is failing.
Could this give the results I am seeing?
Anything flowing through the abv goes through my heat meter but maybe if water is flowing through it, then the heat pump is consuming electricity but just not heating anything.
If water was going through ABV, then you’d have a short-circuit in your primary loop. Flow temperature would rise quickly, and heatpump would cycle like mad. I don’t think that’s happening here.
Then it can only be the heat pump.
The DHW cycle went wrong again today so I stopped it. When I restarted it a few minutes later it is normal again.
It’s weird.
I have contacted Octopus again.
I am writing here just so that if anybody else has the issue there will be somewhere to look.
I have just had a visit from a Daikin engineer to investigate my issue.
It was very strange. I had to endure a bit of a lecture on how to run my heat pump. Apparently I don’t know how to get the best out of it! It’s not possible for me to get enough heat for the house from 30c water when it 0c outside, I must be cold or have to turn the flow temperature up as it gets colder. My data is inaccurate as what we see does not make sense to him so cannot be true.
My heat meter is not 100% accurate (OK, true). What he thinks is that the heat meter is accurate most of the time but sometimes not accurate at all!
The explanation of this
It’s performing really well he says as the flow temperature is building, so even though it appears not to be producing as much heat as normal, it must be because of the amount of electricity it is using.
He explained to me that there is a calculation I could use to establish the heat being produced, he couldn’t understand that this is what the graph shows. He said it must have been producing more heat than shown due to the electricity consumption and the way the flow temperature was rising.
I asked him to explain why the dT was only 2c when it is normally 3.5c.
The answer was that it didn’t matter as the difference was only 1.5c, so very small and within the accuracy of the heat meter!
It was really frustrating and he refused to look at the heat pump as its working (heating and DHW) with no error codes.
Astonishing really.
I am the only person he has ever met who is interested in stuff like this and really I should spend less time looking at it and just let it do its thing.
Daikin don’t like customers to have too much information as they don’t need it and most of them would find it confusing.
I forgot the funniest thing he said.
Heat Geek installers only get good SCOPs by ‘cheating’. Apparently, they ‘cheat’ by only designing and installing heat systems to run at very low flow temperatures just to get a good SCOP leaving customers with not enough heat when they need it.
I cannot think what is causing this, if anybody has any ideas I would love to hear them. This can’t be right. This is 03 October 2024.
It’s curious to see in that last run there’s a change in behaviour at 15:30 when both the dT and the slope of the temperatures go up inline with the increased heat output. Hard to see how that could be result of an “inaccurate heat meter”.
I wonder if @johncantor has any insights on the charts in this thread…
Hi Matt, sorry, not been on the ball with your one. Its really odd. I assume that flat line is the flow rate? well… surely the inaccuracies we see with meters is due to inaccurate flowrate sensing. Yours looks spot on. As you say Ken, The heat meter looks OK. we are seeing here a roughly constant input power, and constant flowrate. then we see the dt widen for the last 5-10 minutes.
Is there any way you could get a temperaure sensor on the dicharge pipe (the small hot one) out of the compressor? It would be interesting to see how that changes. Is there anything unusual about the refrigerant circuit design? one expansion valve? Is this pattern repeated anywhere? i.e. does it ever go from good-bad (as opposed to bad to good here) . Can you point me to you on HPM? There will be a reason… we just have to puzzle it out
I had only looked at the while-running area. I cannot see the flow & return temperatures coming together as you would expect when the compressor stops.
Matt’s system on HPM is https://heatpumpmonitor.org/system/view?id=72
Here’s a link to the DHW cycle on Oct 3rd: https://emoncms.org/app/view?name=MyHeatpump&readkey=bbd1cd04728bd8c9f7acfb2ee51936d2&mode=power&start=1727963370&end=1727967590&flow=1&carnot=0.5
And October 9th: https://emoncms.org/app/view?name=MyHeatpump&readkey=bbd1cd04728bd8c9f7acfb2ee51936d2&mode=power&start=1728481780&end=1728485410&flow=1&carnot=0.5
Did you ever get the ESPAltherma or p1p2Serial hooked up.
It would be interesting to see what the MMI is saying when we see these figures (does the ASHP believe it is maintaining a DT of 5, are you seeing the same values for flow and return from the outdoor unit) Is the heat being lost somewhere on route between the ASHP and the meters or is it not being generated in the first instance. You would expect this more pronounced on DHW then space due to the temperatures involved.
Do you notice any heating in the space circuit or the pipe past the three way valve when the DHW is running (partially stuck Esbe valve?).
Has some of the lagging split / opened up and it is trying to heat the pipework and only when the pipework/ surrounding insulation is heated does it push all the that to the tank?
Bit of a cop out from the Daikin engineer and sounds like he needs a few refreshers on thermodynamics and hydronic design but similar to my experience (where the engineer categorically told me no updates were available then plugged into the unit and found two updates 
).
Thank you very much for the replies @Timbones @KnightPhoenix and @johncantor
I will address the points in order
@johncantor Yes, the blue straight line is the flow rate, steady at 24lpm as normal. I never see any issues here.
I also have the simulated carnot heat output showing on the graph here.
My flow and return temperatures do converge and meet perfectly every time the compressor is off
I see no issues with the heat meter and I am confident that the electricity meter is recording correctly as it corresponds to other data from my solar inverter.
I think my data is accurate.
I may be able to check the temperature on the discharge pipe as I do have clip on thermometers.
@KnightPhoenix Hi Zak, hope you are OK.
I have not hooked up ESPAltherma or P1P2 serial yet, but I really should.
I never see a dT of 5c on the DHW although I got the impression from the Daikin engineer that this is what it should be and he thought there was some adjustment but I have never seen it and haven’t really looked for it.
I haven’t noticed any space heating when DHHW is running and I sit right next to a radiator that I do feel a surge of heat from when the 3 way valve switches back to space heating at the end of the DHW cycle.
There is no change in pipework or lagging. I would think the heat meter would still pick up any heat lost though?
Generally.
The problem is intermittent, some days fine, other days not.
The DHW seems erratic even when working normally.
The heat pump seems to lack a bit of punch at the beginning of a DHW or space heating cycle, it doesn’t feel like it did at the beginning if that makes sense.
I first noticed the issue on 14 September 2024 with space heating, loads of electricity and not much heat. The graph is at the top of the page.
The heat pump is generally running well, although as I said, it `feels’ different to it did before the summer.
It did have a firmware update in May 2024.
One other thing I have noticed. I run a fixed lwt and just set it wherever the heat pump runs best. This used to be 31c when colder and 32c when a bit warmer, say +10c and over.
Now the heat pump is running best at 33c flow.
The issue when running DHW is odd and intermittent but when it goes wrong it seems to follow the same pattern, something seems to `release’ as the flow temperature builds and I if I notice the problem I can correct it by ending the DHW cycle and restarting it.
The only thing that has changed recently is I fitted an OEM DHW sensor module on 22 August 2024. Maybe something is interfering with the operation of the 3 port valve.
I will recheck my work 
It is very puzzling indeed. I just had a look over the last month. The flow rate readings look good. It seemed at first as it the problem only shows up when flow rate high, but there are several instances if it running fine, then the input power rises, and the flow temp drops (with constant flow rate)… this drop is odd. (e.g. 00:15 on 11th) Somehow, the heat output drops at cetain times, and usually happens at startup, but can happen during running. The odd thing is the rise in power input, with no increase in heat output. Could this be liquid refrigerant entering the compressor?? there are times when it regularly does this when space heating. A sensor on the compressor inlet and compressor outlet (several inches from the compressor) would tell a lot.
Thanks John,
I’m no expert so I may make mistakes!
I had so much trouble with the previous heat pump that I spent a large amount of time just watching my data and it is a habit that I am trying to get out of.
Based on this, I just have a feeling that the heat pump is generally not quite right although most of the time the efficiency is very good. I am happy with that, of course, but I just `know’ something is wrong.
The DHW graphs make the problem most apparent but I also feel the heat pump has lost its punch which I feel on start up.
So, now the bits I don’t know enough about.
If liquid refrigerant is entering the compressor how might this happen and what problems would it cause?
If liquid refrigerant is entering the compressor when it shouldn’t be, then it refrigerant being lost to the atmosphere, leaking?
Is it possible for something to leak/pass liquid when it shouldn’t but only at certain times?
Maybe the compressor is leaking when it is cooler and seals up when it has been running a while?
My usual experience is that when something is wearing excessively or broken, it doesn’t just repair itself.
My real concern is that failure of some component is on the horizon.
And how to convince Daikin that there is a problem!
re flow rate for DHW, and the close dt for DHW. It can be useful to have a gate-valve in series with the DHW coil simply to slow the flowrate a bit. Often, the pump is set to give adequate heating flow, then this can be too much for DHW. with a tall coil in a tank, i would not think a very close dt is helpful. However, most manufactureres seem happt with high flowrates on dhw. a resticting valve (not lever type) might be helpfull… or not
It won’t be a loss of refrigerant. It’s working well occasionally, so will have a full charge , no leaks. IF the expansion valve opens too much, it could ‘flood’ the outside heat exchanger, and instead of just vapour entering the compressor (as normal), it could be part liquid. Its just a theory that this could be happening. More temperature sensors should prove/disprove
Hi John,
Thank you for your help.
I do have a tall slimline tank and was thinking that perhaps the flow rate was too high, or could be reduced to widen the dT I am seeing.
DHW has always been a bit `choppy’ and I don’t think I really ever saw great performance on DHW with the 9kW Daikin unit. I have the same tank and valves/pipework, so there is some correlation here.
But I have not really noticed anything as extreme as I have recently.
Comparing to other Octopus Daikin installations with similar tanks I have always felt my DHW cycle under performed.
Do you know what would cause the expansion valve to open too much?
If I put temperature sensors on the compressor what am I expecting to see?
This is the evening of 10/11 October that John mentions. At this time the flow temperature was set at 32c but I see a steady decline in the flow temperature. I see this quite often and don’t really know why it happens. These particular Daikin heat pump all seem to have an erratic flow temperature, it is rarely steady.
It could be the expansion valve (eev) sometimes opening too much. It could be a sensor as part of eev control. It’s unusual, so I’m not sure it’s your prob. When the output ‘dips’ due to liquid entering compressor, the discharge temperature drops to about the same as the water flow temperature… This is not good. The suction sensor will probably tell us nothing unless very accurate… Actually, it might be better to fit it after expansion valve. I have seen similar expansion valve issues with my 6kw ecodan. I could show you similar ‘crashes’ in output
Thanks John.
I think I understand.
I am not losing refrigerant which is good.
Liquid refrigerant entering the compressor is not good, does it damage anything?
I know you can’t compress a liquid so liquid in a compressor sounds like a problem to me?
To identify the problem I guess it would only show up as a fault when it is actually happening, so I would have to have test equipment fitted waiting for it to happen and some way of logging the data?
I did suggest to the Daikin engineer yesterday that I suspected a fault with a valve controlling the refrigerant but he refused to look as he didn’t think my data indicated anything amiss with the heat pump.
This is really beyond me and my skills so I need to think what I can do about it.
in the past, liquid entering a compressor was very bad and detrimantal, however, new designs apparently will cope with liquid. (there is a good mitsubishi video somewhere). My ecodan has definately had liquid entering the compressor
