@jamespa Thanks again for this info.

Just by way of an update, I’ve spoken to Mitsubishi support today and while they wouldn’t commit to anything because they’re obviously not in receipt of all the facts, he did say that a) he’s never seen a 14kWh machine on a single zone install before. And b) the flow rate is concerning. He said he’d expect 40l per hour rather than the often sub minimum 16 or 17 l per hour we’re seeing. 

The R290 does sound like a good option but as you say; I doubt we’ll get the choice if they do arrange a swap.

Looking at the energy usage yesterday the COP is around 2.5 (or 2.9 if just looking at heating and not DHW). 

Sadly the MelCloud charts don’t give you exact figures so there’s an element of guess work.

We seemed to see less cycling over the last 24 hours. Other than it bouncing around between 7am and 8am today it’s been fairly stable.

it was “buoyant” during warmer/sunnier hours yesterday (from 10am to 3pm) though. 

Temperatures are looking warmer over the next couple of days so I’ll keep my eyes on it. My concern is that the $#!£ will really hit the fan when the weather gets warmer.

It may be unrelated but the concerns that @davidnolan22 initially raised about the low flow rate and also Mitsubishi’s reaction would suggest something’s amiss with the setup. 

It does now feel like the size is overkill for this house.

We don’t have a diagram of the tank setup sadly. And I appreciate there’s a lot to try to fit into photos amidst the sea of lagging. 

One thing that did occur to me is that we have motorized valves (image attached) on each manifold. When our original heating engineer was on site a few months ago he said we wouldn’t need that if we had a heat pump. He’s not a heat pump expert though.

Could that be causing an issue with performance?

Thanks for the legal references. I spent ages yesterday searching for them all but I couldn’t find the pertinent ECO4 references so this is all really useful again.

@sandman1600 just for comparison purposes and in case useful as evidence (!) here's my energy usage and flow temps for the same day and same Mitsi 14kW unit:

Posted by: @sandman1600

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One thing that did occur to me is that we have motorized valves (image attached) on each manifold. When our original heating engineer was on site a few months ago he said we wouldn’t need that if we had a heat pump. He’s not a heat pump expert though.

 

If they arent permanently open then yes they would cause a problem (unless they are all wired to close simultaneously when the DHW comes on - instead of a diverter valve.  But I think I saw a diverter valve in the photo.  What opens/closes them, room stats?

Posted by: @sandman1600

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Just by way of an update, I’ve spoken to Mitsubishi support today and while they wouldn’t commit to anything because they’re obviously not in receipt of all the facts, he did say that a) he’s never seen a 14kWh machine on a single zone install before. And b) the flow rate is concerning. He said he’d expect 40l per hour rather than the often sub minimum 16 or 17 l per hour we’re seeing.

14kW is a big machine, the sort of machine you put in houses that are likely to have more than one zone.  However it shouldn't be a problem. 

I assume you mean l/min not l/hr.  14l/min would be normal for a ~6kW machine.  40l/min for a 14kW machine.  I am guessing the installers adjusted it down to get a specific deltaT across the emitters but thats only really a guess.  Or alternatively something in the circuit is limiting it.  But the fact the house is getting hot suggests that you dont need much more!

I note 25kWh consumed for heating, about 70kWh delivered on the 16th, COP as you say ~2.8/2.9.  One day alone is a bit meaningless but nevertheless, for comparison, my figures were 23kWh consumed, 96kWh delivered (COP 4).  Thats for a 7kW house.  

Heating COP 2.9 is a bit better but really you should be seeing better still now its warm during the day.   

Posted by: @sandman1600

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Temperatures are looking warmer over the next couple of days so I’ll keep my eyes on it. My concern is that the $#!£ will really hit the fan when the weather gets warmer.

Costs should get better as it gets warmer.  Heat pumps get more efficient as flow temp falls or OAT rises.

The Melcloud user manual shows plots of various things over multiple days https://library.mitsubishielectric.co.uk/pdf/book/MELCloud_USER_MANUAL_UK1#page-1   It would be really helpful if you got these for the key parameters (eg energy, flow temp, outside temp, indoor temp) since it was installed, preferably, if it will let you do so, on the same scale.