@jamespa 

Thanks again for all that. It makes sense. I do want to get as much data as possible but also concerned that at the end of next week they'll be finishing the entire job (solar panels) and wanting it signed off. I also would rather tackle it before we've had the pump for too long but I can also see that we need to give it some time to gather evidence.

I wonder if Mitsubishi support would offer an opinion on the graphs? If they were willing to state that it looks oversized, it might be ammunition.

We did tell the installers about the upgrades to the EPC but sadly, as with most key information we told them about the house, it seems to have been ignored. 

I will keep working on lowering the WC flow temperature daily now... but it does look like since lowering it again this morning, the flow temperature is bouncing all over the place again. I've attached a few more graphs below. There's also a pie chart of the operation mode for the last 24 hours and it looks like 17% of the time, it's been off. So does that suggest cycling?

I can't see anyway in Melcloud to view anything other than hourly graphs. I've checked the Octopus app this afternoon and I'm amazed to see that the first full day of weather compensation has seen a drop in energy usage despite having the pump running 24/7 and having a really warm house. I mean, there's a long way to go before we get it to the right flow temperature but even so, I'm amazed.

I'll uploaded photos of the water tank in a separate post. Excuse the state of the place. It will be all boxed in one day.

@jamespa The tank...

I think you’ve got a piped header , not a buffer.

The called for temps are now low and you are cycling the machine. The fact that it’s cycling at temps of 5 OAT and below means, im pretty sure, you are well over sized. 

the flow rate is very low for the 14kw pump, the installer set that flow rate, so they seem to know you don’t need much heat.

Post more data over the coming days, but I think you need the 6 or maybe 8.5kw machine

but please don’t quote me! 

@davidnolan22 Thanks David. It's so frustrating because I can finally see the potential of heat pumps but I feel like being lumbered with an oversized unit is such a cause for concern.

It was a pretty cold day here yesterday. Frost overnight. So I'm impressed that the house was kept so warm. I mean, to wake up to a comfortable house is fantastic. But yes, it's definitely not optimum performance.

I've got the WC set to -3/43 now... so if I moved it back to a fixed temperature of 45, isn't that going to just use loads more energy? Oh but you're saying run it for only 10 to 12 hours instead of 24/7? 

My worry there is that we're going to be giving up the constant warmth for peaks and troughs throughout the day.

Thanks for the heads up about the cycling. I've seen a couple of rules of thumb online and most seems to point to 8.5 being a good option for our size... certainly not 14. Gutted. Fingers crossed I can get them to see sense.

Thanks again. The advice from you and James is just brilliant. I wish I could send a virtual pint your way.

Posted by: @sandman1600

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We did tell the installers about the upgrades to the EPC but sadly, as with most key information we told them about the house, it seems to have been ignored. 

That's important.  Hold onto it, gather any evidence.

If somehow that can be combined with operational evidence then you may have a chance.

Does melcloud display oat somehow?  Ideally on the same plot.  Oat plus a cycling system might prove it's oversized.  Does it cycle at say 6, 7 C?

I didn't realise installation is still ongoing: that puts you in a much better position.  Very likely they don't get paid until you sign.  They will therefore attempt to bully you into signing, if possible don't be bullied.  Have they done a handover of the ashp and given you proper instructions, if not then that alone is sufficient 

@sandman1600 

It’s tricky, if you run it in the 30s, it will cycle a lot. If you run it in the 40s, it will cost a bit more to run and you will have to run it more on/off which is not ideal for a heat pump, but I think your actual heat loss is a lot lot lower than you think and youre going to have to compromise. 

the one thing you 100% cannot do is run zones. With your heat pump, you have to run it as open as you can, everything open always.

if it was mine, I think I would run it fixed flow and more on/off, initially to get more data and a feel for heating and cooling. For instance, if you run 45 fixed flow for certain hours, how does this heat the house at what outdoor temp and how long does it hold that temp for.  You’ve going to need to really get a feel for this. 

But if you can get the UFH plan from when you had that laid it will help with outputs.

it took me ages to actually get control of my unit, run tests and then sort it out myself. But, I honestly think youre going to come up against the limits of a 14kw heat pump in a house that might only be 5kw heat loss (educated guess!!!)