@editor Just seen your book 'Bodge Busters' with a forward by Graham Hendra. Graham Hendra formerly of Freedom Heat Pumps who supplied the Hitachi system to our installers including all the parts I now know have no place in a heat pump system. Low loss headers, individiual room thermostats etc.

Posted by: @sim0n0

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@jamespa Latest issue is the system getting 'stuck' in hot water mode and not switching back to heating. The motorised valve can be operated manually.

What does the controller show - does it show that its in heating mode or does it show its in dhw mode?  It could just be a stuck valve/faulty conection

@editor Big ad on this site advertising £7500 saving on a heat pump. NOT if that £7500 went to the developer! As the first owner of our property, I was forced to pay serveral thousand pounds to rectify an incorrectly designed and installed system.

@jamespa I honestly do appreciate you trying to help but it's nothing obvious. It's in DHW mode which is set to 48 degrees - temp gets up to 48 but it's not switching back to heating. If I turn heating and DHW both off, then turn them back on, it starts working again. The Honeywell value is operating normally so it must be controls/wiring related. I've turned DHW off and switched the immersion on 24/7. I'll look into a different heat pump brand in the new year...

@jamespa I guess it could be a faulty connection. The original installers fitted all the cables so badly that the mental case wouldn't fit. It's sat on the floor of our plant room ever since

Check on the heat pump controller.  It will show whether the heat pump thinks its in DHW or space heating mode.  If it thinks its in the desired mode then the problem lies with the connection or the valve and any plumber can fix it.  If it thinks its not in the desired mode then its a configuration problem.  If it once worked and you haven't changed anything then its more likely to be the former than the latter. 

This isnt a particularly heat pump specific problem unless its very obscure, which is highly unlikely.

Its a pity if you end up replacing it, judging by the manual its a good piece of kit.  Too far away for you, but the installer who did my heat pump is happy to have a go at any make.  Maybe there is someone locally who will do that for you.  For the most part heat pumps are heat pumps just like boilers are boilers.  They all have similar features and operate according to the same laws of physics.  Once you know one you are 80+% of the way to knowing many others.  This particular problem will fall in the 80% category & its anyway easy to diagnose using a multimeter and a bit of brain.

@jamespa My experience is that local 'old school' plumbers/heating engineers tend to be older and don't want the hassle of getting involved in poorly designed/installed heat pump systems. Mention Hitachi and you just get a dial tone. There is no UK support for Hitachi and no local engineers are willing or able to service Hitachi.

@sim0n0 

Here's a reply to help you out.  As a owner of the same kit would like to hear more from you.  Hopeful you will be able to message, or just post on here.

Posted by: @sim0n0

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@jamespa My experience is that local 'old school' plumbers/heating engineers tend to be older and don't want the hassle of getting involved in poorly designed/installed heat pump systems. Mention Hitachi and you just get a dial tone. There is no UK support for Hitachi and no local engineers are willing or able to service Hitachi.

Understood.  Nevertheless this is, with high probability, a very simple and easily pinpointed fault that very likely doesn't require any hitachi specific (or even heat pump specific) knowledge to fix.  Perhaps you could do some fault localisation yourself. 

Question 1 is, when the valve fails to switch back to space heating, does the controller show water heating or space heating.  Question 2 is, if you leave it until the end of the programmed time for DHW heating, does it switch back and what does the controller show.

Otherwise perhaps a hitachi (commercial) aircon person might take a look at it?

@jamespa Hi James The controller shows it’s still in DHW mode despite reaching the set temperature. It’s not on a timed program, it turns on at 45 and off at 48 - 24/7. It’s always worked fine until the other day I noticed the house felt cold. If I turn the controller off > on it instantly goes to heating mode and the valve moves accordingly. The issue is it’s reaching 48 degrees but not triggering the return to heating mode. Regarding a Hitachi aircon engineer trust me I’ve tried. Generally though my experience contacting aircon/commercial engineers is that they don’t want anything to do with domestic heat pumps. I suspect because they know the industry is full of cowboys and they don’t need the grief…

Posted by: @sim0n0

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The controller shows it’s still in DHW mode despite reaching the set temperature.

OK, how do you know its reached the set temperature, and does it continue to heat the DHW at an elevated flow temp (and thus overshoots the DHW set temp)?  If not what does it do (switch off entirely, or what else)?  Do you observe any other symptoms?

Are you saying the behaviour has only appeared recently and that no changes were made to any control before it appeared?

Posted by: @sim0n0

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I suspect because they know the industry is full of cowboys and they don’t need the grief…

The whole construction industry is full of cowboys, heat pumps are no different!

@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