Welcome to the forums.

It’s clear that you’ve taken the time to understand your system, and you’re asking all the right questions. I want to start by affirming that you’re right to be a bit concerned: a COP of 2.4 in mid-April, when outside temperatures are relatively mild (even during this cold snap) is suboptimal. It’s also worth stating up front: yes, there is a direct correlation between COP and running costs. The lower your COP, the more electricity you need to achieve the same amount of heat, and that directly impacts your bills.

A COP of 2.4 means that for every 1kWh of electricity your system consumes, it’s generating 2.4kWh of heat. If another system achieves a COP of 3.5 under the same conditions, it means it’s delivering nearly 50% more heat for the same input cost. That translates into higher electricity bills for the same level of warmth in your home. So yes, if your COP is low in milder months like April, you could indeed see a sharp rise in costs during colder winter months unless the underlying issues are addressed.

Can you confirm whether a buffer tank was included in the installation? I assume it was, given standard practice for radiator-based Ecodan installs.

Your flow rate has dropped from 24L/min to 21L/min since commissioning, which could be indicative of a developing circulation issue… perhaps a clogged strainer, partial airlock or early fouling in the system. At 21L/min, your system is still functioning, but lower flow can result in less efficient heat transfer at the emitters, which in turn may prompt the heat pump to ramp up flow temperature unnecessarily.

I’ll let other Ecodan users chime in on the Ecodan related stuff.

Hi @editor - thanks for your reply. A buffer tank was not fitted - I was advised in the surveys that buffer tanks should be avoided where possible as they reduced efficiency and that for my system one would not be necessary. I had a few different quotes one or two with buffers, one or two without and went with an install that did not include a buffer. For reference it's a 3 bed house around 150m2 so we're not talking a massive property.

A few other questions/thoughts:

Are installers supposed to do a full flush on the heating system when they install the ASHP and cylinder? I know my system wasn't flushed. Can this impact the warranty at all? I did wonder if perhaps the decrease in flow rate could be the filter getting clogged but this seems to have happened very fast and it's kind of weird the flow rate hasn't changed beyond 21L/min.

There is an automatic bypass valve between the flow and return as I assume is found on most systems. It can be set between 0.1 and 0.5 bar by rotating it. Currently set to 0.3 bar which I assume is fine. I was wondering if there was any way I could be getting leakage between flow and return which could be reducing efficiency but this feels unlikely.

On the weekend I took a radiator off the wall to give it a clean out. It wasn't getting hot low down/in the middle and I wanted to verify that this wasn't caused by debris inside. The massive amount of black gunk (I assume magnetite) that came out of it did surprise me but having given it a good clean with the hosepipe when I put it all back together and bled/pressurised the system this didn't seem to make any difference (next on the list to fix this is larger pipework to the rad but that's likely a weekend project for later in the year).

I haven't yet contacted my installer about the low efficiency - I thought I'd start here to arm myself with some more info first - but they're going to be coming back to install some solar PV in 6ish weeks time so I'll be having plenty more engagement with them (even if it is a different arm of the business). Ironically even though I've always wanted solar PV the poor HP efficiency leading to likely higher running costs is one of the reasons I've just decided to pull the trigger on it.

@cbrenewable Your COP does appear very low and if you don’t have a buffer that rules out one possible cause. The only thing that stands out as unusual is your DT which I would expect to be a bit higher. 

Are there any obvious things like lack of insulation or long external pipe runs that could be losing you heat? 

Im not a melcloud user but you might find this link useful. 
https://community.openenergymonitor.org/t/estimating-power-from-melcloud-data/26767/7

@CBrenewable

A COP of 2.4 is definitely low and you are right to be concerned.  You should be seeing 4 or better at present.

Can you tell us something about the house (floor area, construction), 

Are you absolutely certain that there is no buffer tank, plate heat exchanger or low loss header between heat pump and emitters, sometimes they are 'included' with the DHW cylinder, and its very common to add a PHE if you are using glycol both to save on the quantity of glycol and so there is no chance of contact between glycol and DHW.

Nothing wrong with running on pure weather compensation and radiators, its what I did for all of the main part of the heating season, I've just switched over to an element of room influence (effectively just limiting) because of solar gain, but will go back to pure WC in the new season because, for me, it results in best stability (and of course best COP).  In any case the first thing that should always be done is to optimise the WC settings by running on pure WC with everything open, even if you then introduce some element of thermostatic control or room influence

What happens if you set the automatic bypass to the max possible value (essentially shutting it off) - thats a test well worth doing - not least because you shouldn't need an automatic bypass if the downstream system is working correctly.

If you are able to post some plots from MelCloud or Melpump that would be helpful.  Also maybe some pictures of the tank and other interesting parts of the installation.

@cbrenewable 

Hi, the graphs from Mel pump would be good. Can you draw your system, have you got a low loss header?  or are you directly piped into the house on one big circuit with one pump? 

@bontwoody - thank you for that link on estimating power usage. Looks like there could be some good tips to help me monitor it which I'll look into further this evening.

The external pipework is only about 1.5m long as the external unit and cylinder etc are either side of a garage wall. The external pipework and all pipework in/around the cylinder (including flow/return) are lagged. When the flow/return go from the garage into the house the lagging stops but it's not a massive house and while I concede this of course won't help I can't believe it could be the root cause here. My property is a 2 story 3bed 150m2 semi-detached so we're not talking crazily long pipe runs to the radiators.

@jamespa - The external unit itself is an Ecodan PUZ-WM85VAA.

I've included a screenshot of the graph from melpump.com (much more informative than the MELCloud graphs!).

I had my DHW in Eco Mode and last night it was quite cold (down to 1C) so ignore the fact the system failed to heat my DHW properly in the window I gave it of 5-6.30am - so far as I'm aware it's just a blip and not something I'm particularly worried about (unless you say otherwise).

As mentioned above I'm aware some of the downstairs rads could do with some larger pipework leading to them as they're not getting uniformly warm - a project I plan to tackle later in the year. This should hopefully help improve DT a bit.

Based off of everyone's confirmation here that something isn't right and I'm not just overreacting I've reached out to the installer this morning, they've agreed it should be operating better than that and they're going to do a bit of head scratching and come back to me with a plan/send someone out.

@davidnolan22 - Please see diagram attached.

*Edit - 1 issue in the initial version of the diagram.

Updated version attached.

@cbrenewable Hopefully the diagram shows one of the valves in the wrong place, otherwise there is a valve in the wrong place.

Any idea why two pumps?

Whats the house construction/level of insulation.  8.5kW is quite large for 150sq m, your heat pump may be oversized which would account for low deltaT (but 2-3 isnt that low)

Struggling from the graph to understand why you would get a COP of only 2.4, its not doing vast amount of cycling (mind you its not delivering vast amounts of heat).  

@jamespa - Property is a 1990ish 3 bed 2 story semi-detached house. Fully double glazed. Only about 100mm of loft insulation which I already plan to do something about in the summer but this shouldn't be impacting my COP too much at the moment I wouldn't have thought? It seems to hold heat reasonably well despite this. Only had the property for c.8 months but no drafts to report.

Regarding buffers/low loss headers/plate heat exchangers - None that I'm aware of (I've drawn a diagram and posted moments ago). The cylinder is a Joule Cyclone CY250L Indirect Hi Gain Coil C if that helps. On the sticker it says 13.2L Heat Exchanger Rated Volume. I definitely have glycol in the heating system as I was talking to the installer as he was adding it near the end of the install.

Thanks for clarity on WC vs Room Influence. When the weather cools off next heating season I very much intend to give pure WC a go as from my reading/watching of HeatGeek YT videos it seems like something cool to play with. Since I've only had the system a week and we're already mid-April I'm not imagining I'll have a chance to give it a proper test this year. My understanding is that Room Influence (Auto Adapt) mode uses much of the same logic as pure WC anyway.

I've set the auto bypass to 0.5bar (max). Not expecting any difference but will see.

@jamespa - yes, looks like I made a mistake on the diagram. I asked for the install to be quite compact in a corner of the garage so it's a little tricky to follow some of the pipework when it's partially obscured by the cylinder. Corrected version attached.

Worth clarifying that both valves are set to auto. I assume these are working correctly since my DHW temp doesn't show any anomalies when the system is heating.

Posted by: @cbrenewable

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@jamespa - yes, looks like I made a mistake on the diagram. I asked for the install to be quite compact in a corner of the garage so it's a little tricky to follow some of the pipework when it's partially obscured by the cylinder. Corrected version attached.

Worth clarifying that both valves are set to auto. I assume these are working correctly since my DHW temp doesn't show any anomalies when the system is heating.

Great. If you could post a picture of the area around the cylinder it would confirm that there is nothing untoward here.