Crustydoodle

As far as we can tell, every heating zone comes on when the stats call for it, but we haven't really tested how much heat is outputted yet. Might try that now. I do not think we have a buffer. They are larger than an expansion tank, right?

Yeah - my gut feel is that it is just heating whatever is in the loop to the ASHP, possibly something in the UFH loop, but I am very far from an expert. The legionella cycle is set to 60°C but that is on a 7 day cycle, was at 5am but now at 2pm Other temp settings from the summary: Hroom1 30°C HFlow1 55°C Croom1 20°C Cflow1 15°C HWtemp 50°C HWDRop 10°C

Nope, when the heat pump is running on those activations hat happen every 2-3 hours, it is not trying to heat anything as far as we can tell. The flow and return temps rise up, but this is not affecting the DHW and the heating is off. This happens around 8 times per day. When there is a call to heat up the DHW, this also activates the ASHP and the cylinder temp rises back to 50degC - this happens around once per day. The reheat threshold is 10 degC below the 50 and that seems to be working fine. Traces of the two types of activation we see are attached - First image is a normal hot water call and you can see the red trace for the hot water temp rise. Second image is one of the random activations where the overlapping flow and return temps drop to ~30degC, then dip and rise together to ~60degC - no call for heating or DHW.

Thanks for this - we tried it last night but it didn't change the behaviour. I was optimistic as it definitely seems to be the drop in flow/return temps that drives the ASHP to come on - usually around 25degC. They have become more frequent with the weather cooling.

I believe it is. That pump comes on when there is a call for hot water and circulates the tank (I think). When the random ASHP activations happen every couple of hours, it does not come on - the one that activates is the black one in this picture which is on either the in flow or return from the ASHP (although I am struggling to get to it to confirm that!).

One other thing to add - we have had the installer back twice, the second with a specialist. They thought it was resolved but as they went to leave, the ASHP was on, which they agreed shouldn't be the case. They spent a chunk of time on the phone to Mitsubishi who claim that it is normal behaviour - It does not sound like it to me from the comments so far.

@ProDave Is there an easy way to check for that? We just had a slightly different symptom - I could hear the pumps working water around the system and yet the ASHP was not active according to the app - I can hear noise where the UFH loop would come down. Up in the loft by the system it is definitely not running, yet I can feel a small vibration on the return to the ASHP where that pump is and also the spitter - hard to tell where else. The noise of water moving was also loud by the ASHP itself and yet the ASHP was not actually running.

Hi all, I am new here so hopefully posting in the right place and this is OK to ask. We have recently had the following installed: Mistubishi Ecodan R32 11.2kW Mitsubishi FTC6 controller Underfloor heating throughout (Heatmiser controlled) The Mitsubishi cylinder is horizontally mounted in the loft as shown in the picture. We are seeing a behaviour which our installer said should not happen and yet Mitsubishi claim is 'normal'. Every 2-4 hours, the ASHP will activate when there is no call for hot water or heating (and no legionella cycle). The Hot water calls appear to be normal and happen as expected. We were told that the ASHP should only really come on at the moment when the hot water needs bringing back up to temp. This is clearly not the case and now the installer is backtracking following a call to Mitsubishi. I've complied a full day of hourly traces into one image (attached) that shows these spikes in the form of flow and return temperatures spiking, then gradually dropping and then triggering to spike again when it hits around 25degC. On this trace you can also see a hot water call and the cylinder temp rising to the correct level. We also tested the heating last night so you can see some activity around that. We can also hear that water is being pumped through the services in the wall on the internal side of the setup - not sure if it is requesting water or wasting water or both, but it is coming from where the mains connects into the ASHP setup and where the ASHP connects down to the UFH manifolds. As a side note, we did have an L9 error as well but this has not returned and so we think it is not related. The main issue is that the pumps and water movement in the loft is noisy enough to wake us in the night. We are very tired! I am not convinced this is normal behaviour - if it is, then we have a major issue with constant noise through the night. The 2 other Ecodan users I know do not see this happening. Any ideas or seen this behaviour before? Thanks in advance