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Ecodan ASHP cycling every couple of hours

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(@derek-m)
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Posted by: @crustydoodle

@derek-m that’s more of less right.

When I turned on the heating, the actuators opened but no pump came on.  Only 20 mins later the primary water pump and then the ASHP came on. 

i had considered the installer competent - they were recommended by someone we know and most of the work they have done seems good.  There was a loose cable to a pump, but things happen.  However, not being able to diagnose this issue is a concern, especially if it does turn out to be the UFH control connection to the Mitsubishi control.

the other area that has knocked my confidence in them is there being no flagging of noise concerns with the tank location.  Even if it does get sorted, I think the noise from the circulating pump is going to be an issue.  

From the noise point of view I seem to think that the water pump is being supported by the pipework. The pump should be mounted on a suitable bracket with vibration absorbers if necessary. The water pump should also have a thermal jacket which it may be possible to get from the pump manufacturer. Besides reducing heat loss, it may also help to attenuate any noise from the pump. All the pipework in and around your loft should be adequately supported and insulated.

If you are not happy with the installation then call your installer back. It is only by people questioning the quality and complaining is there any hope of installations improving.

 


   
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(@crustydoodle)
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Topic starter  

@derek-m Thanks for all you input.  We are piling pressure on the installer to get this sorted.  We are also just trying to be proactive in finding out the possible causes of the issue.  What I was most curious about is whether other Ecodan users have seen something similar to back up the suggestion from Mitsubishi that the ASHP is operating normally.

I am hopeful that the installer will rescue the situation.  Things go wrong and mistakes can be made but how they respond is the important bit.


   
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(@derek-m)
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@crustydoodle

The installer is responsible to provide you with a proven functioning system, failure to do so would be a breach of contract. I would suggest you ask them to prove that the system is functioning correctly.


   
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Morgan
(@morgan)
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I have the same heat pump (Ecodan 11.2) as a retrofit to radiators. Been running since November 2021.  It's pretty much silent.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.


   
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(@harriup)
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@crustydoodle 

The system as a whole is definitely not operating ‘normally’, the issue is identifying a problem when a standard bit of kit, the EcoDan, is attached to a unique setup, which everyone’s house is. We only have a bit of information to go on – the installer is in the best position to understand how the system is meant to run – you are in the best position to make what changes you can and observe any effect. I have read that Heatmiser and Ecodans don't play well together so you would hope that that would be on Mitsubishi’s radar and they might have some combined knowledge to draw on to offer the installer potential areas to examine. The temperature records you posted showed behaviour as you would expect in both HW and heating modes when they came on, so whatever is causing the odd running is not preventing normal running.

One change you could try to see if if it has a consequence is adjusting the schedules at the controller to prevent heating and hot water cycles from running at night. Not only should this give you some temporary relief from the pump/water noise but if the outdoor unit keeps coming on despite the restriction then it might help narrow down the cause. If this change prevents the odd running perhaps try only restricting the HW cycle, but to a narrower time window.

The only time I see similar steep rises in flow and return temps is at the start of a HW cycle, however, the image of the controller you posted when the outdoor unit was operating showed the stand-by symbol against both the heating and hot water modes, in which case you would not expect the unit to be asking anything of the pump itself related to those modes. The temperature on the spikes you are getting is pushed to well above the top temperature you have for heating (40°) and a bit above the max you get on a hot water cycle, usually 5° or so above the set tank temp. It reaches 60° which I believe is an absolute limit for the system. Does lowering the target tank temp change these spikes? Does changing the operating mode to Target Flow Temperature alter the behaviour at all?

I would make the following observation about what you have tried so far — a call for heat from a thermostat is only that, a request, it is the FTC that decides whether all the criteria to supply heat are fulfilled. In some of the examples you gave, the fact that the target flow temperature will be around 30° in current conditions means that if the THW2 thermistor on the primary return leg is giving a temperature reading of above 30° this is likely to be interpreted as the heating system needing no extra heat right then. I think it waits a while then circulates a bit of water round and sees how the temps change before recalculating anything. So a lack of response in the pump might not indicate a malfunction.

I see you have the controller stuck on the front of the FTC in the loft, not a great place to have it as it is useful to see what the system is up to and be accessible when you want to make changes to schedules etc. It does come on a long cable, perhaps there is a bit of wall somewhere you can position it on and have the cable run into the loft.

Though the pump model you mention is different to the ones on my Ecodan cylinder they are all Grundfoss pumps, and I found the primary circulation pump to be intrusively loud and unpleasant in tone. I solved both of these by reducing the pump speed setting (though I am not sure if there are consequences I should be considering), it might be worth a try in consultation with your installer. Perhaps boxing the pump in, even roughly, with some solid foam insulation board will mitigate the worst of the sound generation.

I don't think I get any kind of water-related sound at the outdoor unit, just the noise of the compressor clunking a bit as it stops. It could be that the fully insulated pipes act as sound insulation, so that might improve when your lagging is complete. But there are a lot of bends in your pipework which I presume make the flow quite turbulent.

Mitsubishi EcoDan 8.5 kW ASHP - radiators on a single loop
210l Mitsubishi solar tank
Solar thermal
3.94kW of PV


   
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(@crustydoodle)
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Topic starter  

Apologies for not jumping back on here for a while.  I thought those that replied might be interested to know the outcome.  We had what was a pretty rare scenario in the end.  There was induced voltage in the wiring from the NeoMiser hubs to the FTC.  This meant that the demand for heating was seen as always on, but the manifolds were all closed.  So the ASHP would be triggered toheat, then heat up a very small loop of water in the system and shut off.  When the temp in the small loop dropped enough it would come on again.  It would do this on repeat as the call for heat never went away.

We now have an additional relay between the two systems that has solved the problem and it appears to have been running normally for a month now.

It was a pretty hard to diagnose fault so I hold no blame with the installer about it.

However, one thing that has surprised me in the whole process is the amount of things that were deemed out of scope fot he installer and not made clear in the process.  Our builders have done all the wiring, all the plumbing to provide the services, all the lagging - basically all the hard stuff!  For this fault, it was described as a 'good will gesture' to fix it - even though the system would never work without it.  I was quite shocked at this reponse.

Thanks for all the comments and assistance - it did help in getting to the root cause.


   
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 Rod
(@rod)
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@crustydoodle The high temp your water got to looks the same as on my Ecodan when it had very limited volume to work on: once the pump comes on an internal algorithm means it won't shut off until it has run for a minimum of 10-20 mins or exceeded max temperature (60/55-ish). I expected the pump to shut down on limited flow whenever the flow set temp had been reached irrespective of how short the runtime was, but it can't run for that short-a-time, it has to keep going and the temp spirals up.


   
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(@bob77)
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Posted by: @crustydoodle

However, one thing that has surprised me in the whole process is the amount of things that were deemed out of scope fot he installer and not made clear in the process.  Our builders have done all the wiring, all the plumbing to provide the services, all the lagging - basically all the hard stuff!  For this fault, it was described as a 'good will gesture' to fix it - even though the system would never work without it.  I was quite shocked at this reponse.

I found the same thing. I got an ASHP installed as part of an extension and more or less total renovation. Despite getting the installer to come and meet with the builder so they could discuss scope of work, it still turned out that there was a whole heap of stuff that fell in the gap in the middle where each thought it was the other's responsibility!

The upshot for me as the customer was over £1000 worth of unexpected bill for supplying and fitting the manifold, mixer, pump and so on. It's easy to say "Well didn't you check what the installer and the builder were supplying?", but when you don't know much about central heating systems and what bits are actually needed, you have to hope that the tradesmen would have covered that when they talked to each other!

 


   
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