Posted by: @sim0n0

↑

@jamespa I know it’s reached the set point as the set temp and the actual temp are both showing 48 degrees. Usually this would trigger the switch back from DHW to heating mode. I haven’t sat with it for long enough to know if it tries to reach a higher temp but I don’t think it does. Normally in DHW mode the heat pump gradually raises the flow temp to 53 degrees. The immersion then takes over, but this only happens with the Legionella program. I’d have to check but I think the heat pump wasn’t producing heat when I found it ‘stuck’ at 48 in DHW mode. No other symptoms other than the house getting cold.

Yes, only happened recently, the heating and hot water have both been working fine for several weeks and no, nothing has been changed on the controller 

OK.  The interesting thing is that the heat pump is still in DHW mode, which presumably means that the controller thinks the job isnt finished yet.  Thats why I ask if it overshoots.

If the flow temp only gets to 53C is it possible that achieving 48 is 'marginal'?  Has something changed which meant tahat its gone from marginal to to insufficient.

This begs the question - what happens if you reduce the target temp.  It also begs the questions

can you adjust the offset between flow temp and target temp?

what cylinder have you got?

Its difficult to ask all the questions without being there (sorry Im not offering.).  

Is there anything else at all which changed around the same time as the problem first appeared, which might give us a clue?

@jamespa It has always worked with these settings and nothing has been changed which points to a fault somewhere. I haven’t done any troubleshooting yet as I know it will work in manual with the immersion on. I know this works as it’s how we were forced to run it the whole first winter before I had the system pipework modified.

Yes I can adjust the hysteresis and the target temp but all that will confirm is it’s not working and I know that already.

It’s a 300L ‘heat pump specific’ tank I can’t remember the brand.

I honestly don’t want to appear ungrateful but yes I will test connections but then I will want to speak to Hitachi to firstly make sure I’m on the latest firmware and then to ask if they’ve seen this particular issue.

Hitachi support doesn’t exist in the UK - it’s not a long term proposition. I will no doubt switch to a supported brand which is a shame as the Hitachi is a nice spec machine. Even if it’s 3-4kW too big for my property but that’s another story LOL

BTW my old Potterton Suprema boiler I had for almost 25 years with just annual services and the odd circuit board change. It was still going strong when I sold the property 2 years ago. 

The MCS certified heat pump installer/developer who fitted the Hitachi spec’d the wrong size heat pump, fitted a Freedom Heat Pumps low loss heater, multiple room stat not fit for purpose package. Incorrectly sized the primary pipework and delivered a system that was basically faulty from day one. The developer pocketed the £7500 and I’m left to pick up the bill to fix. And that same heat pump installer is now not only MCS certified, but they’re also Heat Geek certified and to rub salt into the wound they use photos of my property as advertising on their website.

So please forgive my tone. There may be decent installers out there but you can count them on one hand and there certainly aren’t any near me prepared to support my system.

.

Posted by: @sim0n0

↑

It has always worked with these settings and nothing has been changed which points to a fault somewhere.

It does but, unless there has been a firmware update, it cant be a controller fault, suggesting its a wiring, connection or valve fault.  But that is unlikely to be consistent with the controller saying its in DHW mode when it should be in space heating mode.

A faint possibility is that the temperature sensor has moved or is at fault, but its difficult to see how that is consistent with the controller showing its reached temp.

Something isnt making sense!

Posted by: @sim0n0

↑

I honestly don’t want to appear ungrateful but yes I will test connections but then I will want to speak to Hitachi to firstly make sure I’m on the latest firmware and then to ask if they’ve seen this particular issue.

Hitachi support doesn’t exist in the UK - it’s not a long term proposition. I will no doubt switch to a supported brand which is a shame as the Hitachi is a nice spec machine. Even if it’s 3-4kW too big for my property but that’s another story LOL

Im not suggesting you are ungrateful.  As you describe it its a weird (and unlikely) fault though which makes me wonder if there are any other clues to be had from close observation (which it sounds like you have been doing)

It does appear from what people here are saying that few Hitachi A2W heat pumps have been fitted in the UK.  The manual suggests it is a highly capable machine, possibly one of the most flexible on the market, but it seems like they haven't built out their support network like some others have.