First things first, @lukewarmbath, and welcome to the forum.

I see this is your first post, so let's see what we can do to help. I also have an Ecodan 8.5 kW so, whilst mine is an R32 model, we should be able to compare and contrast pretty reasonably. I am not one of the best here to talk about heat pump config but there are a few pertinent questions I can ask that should open things up for my more able peers here to comment on.

Given how long the system has been installed, your indoor display should be able to give you plenty of historical data. Have you taken a look yet at how much energy was consumed last year/this year and how much heat energy delivered for same period? I only ask because my heat pump is registering a COP right now of 5.11 whilst a minute ago it was 1.96. Mitsi's reporting of COP is nothing if not variable, so a far better indicator of whether there's a real problem or not is the last year's SCOP. Of course, if the 1.5-2 COP you mentioned actually is the SCOP, that's definitely low.

You haven't mentioned whereabouts in the country you are. A general idea of location might help with recommending a company for servicing that is likely to pick up on the things that seem to have been missed.

You also haven't mentioned whether the system is running in weather compensation mode or flow temperature mode. That is highly likely to affect the heat pump's performance so well worth letting us know a few more details.

I would also say that you seem to have a feeling that something isn't right. That is an important point and something you should only relinquish if we manage to satisfy your concerns objectively. You're getting to know your system far better than we ever could so your instincts are valuable.

Thanks for the reply and the welcome !

Located in Inverness (Scotland)

Heatpump has been running in weather compensation mode for the last couple months. Currently at Flow=32@15 outdoor and Flow= 42@-15. 

Regarding historical data unfortunately the energy consumption and production data seems to have been reset before I moved in to the property. I think this might have been done during a service. I do have data for the past few months though.

Daily Breakdown (Total Consumed KWH, CoP Heating, CoP DHW) for October

Daily Breakdown (Total Consumed KWH, CoP Heating, CoP DHW) for November.  Note: data reading between 2nd Nov and 9th Nov is incorrect as I mistakenly adjusted the return thermistor (THW2) reading resulting in lower than actual reported COP figures. All thermistor offsets are now at 0.)

CoP Heating and Energy Consumed for Heating only by Month

- October Heating COP=2.18 for 309 KWH consumed

- November Heating COP = 1.47 for 201 KWH consumed. (actual values likely higher due to mistake mentioned above)

Let me know if there is any other info I can provide to give a better idea. 

that ASHP is working, from the looks of it, way too hard all day.  I know you know this, but something is not right. where is the heat going?

yup, it is definitely over working. You can hear the compressor running hard continuously when getting up to temperature after a stop or setback, then repeatedly ramping up and down once up to temperature. Both of these behaviors can be seen in the original screenshots.

Ultimately it results in the house overheating to the point where I have to shut it off completely overnight. - I have mostly been running it in the morning and afternoon according to my off-peak rates to avoid over heating. 

I actually had some luck running it in Auto adapt mode yesterday for the first time since the summer. Although it was still running hard, it did seem to start modulating slightly before shutting off when room temp was met.

As I have read in other threads that older ecodans have trouble modulating at lower flow temps or low outside temps, I tried cranking the curve up back in weather compensation mode but behavior returned to normal (ramping up and down rather than modulating to a lower frequency) 

I am probably going to explore using Auto-adapt for now to see if that helps.

My main question at the moment is, should the flow temperature fluctuate so much? Even with a stable compressor frequency, the flow temp fluctuates up and down by 3.5 degrees or more every 10 minutes. This seems to happen regardless of load and temperatures so maybe it is just normal behavior but seems a bit strange to me.

Here is my last 24hrs, its very stable and steady. its likely complex why yours is doing what it's doing and without knowing the set up, will he hard to get to the bottom of it.   Those are quite high temps for UFH. Even when its stable, the compressor is running at 90 odd Hz, that is working very hard.  the graphs look odd to me. you probably need someone to see how it's all piped and working.  are you running zones? are things coming on and off all the time? 

@davidnolan22 

Thanks for the graph. That's really useful!

Agreed, these temps are too high but behavior is similarly chaotic at lower flow temps. First screenshot in thread was for 35 degree flow at ~5-10 OAT and behavior is similar. I will reduce further and get further screenshots.

UFH and RADs are running on a single zone. Piping is as shown below, with only difference being that the RADS and UFH simply split at a T junction to divert the water to each. Only flow control for the RADs is the Lockshield valves. Each UFH loop can be individually throttled - all are full open besides one short loop that is throttled to reduce return temp slightly. They are approx 1.5 - 2.5l/min. All room thermostats are fully open and set so high they will never close. All radiators warm fairly evenly.

At this point I have tried everything including balancing the system, running pumps at different speeds to prevent recirculation through low loss header and also adjusting flow temps. Although I see some minor differences, I think the problem goes beyond simply having an unbalanced system. I feel there is something wrong with the outdoor unit resulting in these unhinged flow temperatures.

Things I have considered are issues with the linear expansion valve, refrigerant or sensors in the system, but I am not getting any errors on the controller. 

Do you know your house heat loss? How many UFH loops you got? How many rads? 

Don't know the house heat loss unfortunately. 

Downstairs UFH: 5 loops (downstairs dimensions approx size 8m x 9m)

Upstairs Radiators: 6 total

• 2x 600x600mm
• 3x 600x1000mm
• 1x 600x1300mm

its a little odd that your UFH comes back warmer than the rads.  normally the other way around. if they are all fully open, the water might be travelling too fast to give out much heat. I'm very weary about getting people to tinker with their systems as I'm not qualified and no idea of your full set up.  But have you tried closing the valves to the flows a bit to slow the water down in the UFH.   whats the area of your house. is it well insulated?  you got an 8.5kw? sounds quite big for your emitters. 

Just to clarify, returning water from UFH is colder than returning water from radiators. Just checked with a infrared thermometer and approximate temps were: 

Flow temp to emitters: 31.5

Return Temp from UFH: 24.8

Return Temp from Rads: 28

Combined return Temp: 27

Would need to measure properly but its a fairly large 3 bed with approximate size downstairs is 8x9m. So say 140m2 total? Seems well insulated modern house: cavity timber frame construction with a rendered block outer leaf.

Its definitely possible the unit is oversized. But at the same time, the return temps look to me to be coming back stable and reasonable. Delta T seems to be in the right ballpark and flow rate is decent. So I just can't understand how the system can be performing so badly. 

I will play about a bit over the next few days and see if throttling the RADs or UFH has any effect.

Edit to add - Not sure if this is important but I have never seen the compressor fully cycle when running - as in fall to 0hz and re-start.