my install has never been that great and always returns a higher scop for hot water compared to heating.
ive followed all the advice vids etc but nothing seems to fix it. installer is now looking into it and might get Vaillant to check the gas level, but it can get the hot water to 60+ if it does a legionella cycle, well back in the summer, but still makes me think its not a refrigerant issue.
Hi Adam,
that sounds really frustrating. Can you share some more info or app screenshots so we can try to assist? Energy usage graphs from the app, the weather curve setting, house details, anything you can think of.
Higher COP for hot water sounds weird indeed, however due to the well documented quality issues of the Vaillant temperature sensors it might just be a measurement error and not an actual defect.
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Sorry for the delay. Ok I’ll post some pics up. House is a 1967 cavity insulated 300mm loft epc rated B 4 bed about 125m2. Before install had lots of issues getting an installer. Was gutting kitchen at the time and one installer dropped out so had to get my plumber to run 28mm primaries and some new 28mm flow return pipes to meet the old part of the house where they T into 22mm. Then rads come off the 28mm and 22mm in 15mm copper.
This is yesterday’s use after the installer reverted the settings back after I tried Havenwise for a few weeks. The consumption is pretty much the same.
This is flow and return temps from the Havenwise backend. Havenwise did say I only have a dt of 2c and had I told the installer. I have pretty sure I have but with them being 40 mile away I don’t think the want to investigate so are looking to get Vaillant out. Other guy on renewable heat forum recons he had the same problem and the Vaillant engineer went through 3 sensors before he found a matching pair.
Thanks for the data. A 2K dT is quite low but can be benign. Im leaning towards your true dT being higher and your heat pump having a particularly bad set of temperature sensors that make dT appear lower than it is, translating also to an awful COP. Can you follow the procudures done in this thread:
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Doing some rough tests today using the test mode to run the circulation pump only i noticed 0.5c difference between the flow and return readings, and every time the flow dropped 0.1c the return did. So I might have a bad sensor pair? This test was with just the circulating pump running and compressor off. I’m assuming the monobloc wouldn’t pull 0.5c out of the return water before it passes the flow sensor?
In which direction was the offset? Flow higher than return or the other way round? In any casey with a dT of around 2K as stated earlier, you’re looking at around a 25% error im COP. Note that it would be plausible to see different impacts during DHW and heating as the sensors do pick up ambient heat even in the best of cases and the higher temperature of DHW runs adds an additional distortion to the measurements.
You’re correct, this is fully internal to the device, there’s no way for such a huge drop to manifest.
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Ok just ran the test again and defo 0.5c on return higher than flow maybe 0.55c as sometimes it has 0.6c for a short time.
OK, so your COP is definitely underestimated by 25%, but even accounting for this does not explainba COP of 2.19. What’s your flow temperature?
CoP of 2.19*1.25 for that day could indeed be plausible, if in constant defrost. It’s been 100% RH here for the last few days, defrost danger zone.
True, I keep forgetting you guys live basically under water 
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As a first step, I would swap the sensors around and see what happens to the CoP. It’s trivially easy to do, just need a Torx T20 (iirc) to remove some the outdoor unit case. And be sure to power off the outdoor unit using the circuit breaker.
ive done some rad balancing and possibly made things worse. as house feels cooler. what dt should i be targeting as most rads would only manage dt4 before the lockshield started to affect the flow. on the heat pump the dt doesnt seem to have improved but i do have 2 rads and plinth fan coils to do, just dont want to waste time doing it if im making it worse. maybe i should open them up to match the heat pump dt of 2.8? (thats using the 0.5c correction). yesterday the flow temp was 34-36, its now about 34 but seems to be cycling about once per hour.
where i live in some places i think its below sea level. it used to be marshland like Holland.
