First question is, why is it driving her mad, and why does she consider it a fault?   

Is it just cycling on and off to meet demand which, at this time of year,will be less than it's minimum output (and thus it will definitely cycle).  A boiler would do exactly the same.

Is the house comfortable?  If so what's the actual problem?

Does she just need reassurance?

@jamespa um she says the heating is turned off & it still does this on holiday mode!

Posted by: @profzarkov

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@jamespa um she says the heating is turned off & it still does this on holiday mode!

How/where is it turned off?  Has she got third party controls?  Is it only doing this at night?  What does she mean by 'coming on'?  Holiday mode generally maintains a low temperature, it's not the same as turning off. It's still pretty cold at night so even in holiday mode I wouldn't be surprised if it turns on from time to time.

Heat pumps are way more intelligent than 20 year old boilers (new boilers are also way more intelligent than 20 year old boilers).  Expect unexpected but actually sensible behaviour!  That said if there are third party controls involved (are there?) there is a risk of silly behaviour

The probability that there is something broken is small, more likely it's an unexpected but sensible behaviour, or a (not necessarily sensible) result of conflicting controls.  To work out which we need to know a bit more about the system.

I have a Grant Aerona 290 15.5kW air source heat pump with the latest Grant Smart Controller.  The controller does not have a holiday mode.  In fact I have raised this with the Grant UK Service Desk.

My heat pump has turned off only 7 times in the last 24 hours.  I suspect the flow temperature in your neighbour's heat pump is fixed at a value that is too high.  Therefore, the heat pump heats the water too hot, the room reaches temperature and then the room thermostat turns the system off.  This is a very inefficient way to run.  

She needs to implement weather compensation.  Which I would be happy to explain.  She also needs to run the domestic hot water only a few times per day for an hour each time.  Otherwise, the schedule should have it turned off.

It would help to know whether she has an Aerona 3 (R32 refrigerant) or an Aerona 290 (the latest model with R290 refrigerant).  It would also be good to know whether she has the rather antiquated old controller (Aerona 3 only) or the rather good new Smart Controller.

I would be happy to do a video call with both of you, if that would be helpful.

Many thanks for your replies. I will enquire further.

Hello chaps 

I have an update.

My neighbour had the Grant ASHP & cylinder installed along with the Heatmiser system plus several wireless thermostats. She has a manifold with underfloor heating.

They had a poor handover & no literature at all.

Even though the thermostats are not on demand the system fires up - see photo.

I think she needs to engage a local heating engineer to work thru this & to ensure it is all working. It did work fine for the first year.

I attach some photos  not sure they help?

Steve

Thanks for the info and pictures.  They tell us s lot.

As I suspected she has too many independent controls fighting each other.  Basically too many bosses.  Sadly a large proportion of heating engineers won't have a scooby how to approach this.

The solution is to disable most of them by turning thermostats/trvs/mixing valves to full and setting them to operate 24*7, then use the grant controller alone, setting up weather compensation and balancing.  Also if there is a secondary water pump (because a buffer or low loss header has been fitted) that will need to be considered.

That's a radical change which she may struggle with initially but is the only way ultimately to make it work both sensibly and efficiently (and most comfortably). There are also ways to make it work more or less sensibly but less efficiently and less comfortably that involve a less radical change.

Happy to provide further advice but only if she is prepared to stay the course and forget  everything she has learned about running heating 

Otherwise I wish her the best of luck finding a heating engineer who can put her on the right course.  They exist of course, but there are lots out there who just can't think through multiple control systems acting in parallel and thus in conflict.  Fundamentally this is not a heat pump problem, it's a control systems problem where the problem is too many independent systems.

Thanks. It's pretty much as I figured - too many controllers! Plus the underfloor stuff is also a bit weird.... Cheers

Posted by: @profzarkov

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Thanks. It's pretty much as I figured - too many controllers! Plus the underfloor stuff is also a bit weird.... Cheers

Heatmisers with multiple room stats seem to be endemic if what people post here is anything to go by. I have a feeling that ufh installation and heating installation are two separate jobs the installers of which don't speak to each other, and thus both think they need controllers.  They don't of course, but who cares, the customer pays and is no wiser until it's too late and the installers get to make more money 

I wonder if a lot of these installs and complex control strategies are based on what the customer demands as well, because most people think that the ability to [try and] independently control each individual rooms temperature and schedules is (a) better and (b) saves money. They have no idea about importance of flow rates, cycling, and thermal dynamics and heat losses of buildings. Ignorant plumbers masquerading as heating engineers don't help either for sure.

We visited an ashp install that we spotted just down the road from us before we had ours put in to ask them about it, and this was the thing the home owner complained about- controls. They had to leave it on all the time in winter they said. They had no traditional thermostat that they could turn right down when they left the house, and turn it back up again when they came home.

I asked them if their bills were ok and they said yes- very good, but we don't want to leave it on all the time. Their house is tailor made as well- completely renovated with good insulation all round, with dedicated plant room.

I noticed a few days ago that they've now taken it out and put a gas boiler back in. It is probably costing them more money but they are no doubt happier just because they can employ their set back strategy. Bizarre. 

Thanks for all the replies. I do feel a bit sorry for my neighbour. Not exactly an old lady but retired & on her own. I'll endeavour to help her sort it out. Despite having a degree in physics, I too have puzzled over the concept of "just leave it on". It's an ingrained cultural thing. I have a friend in the next village who regrets having his Eco4 install - free solar & ASHP. He is still of the mentality of getting up & switching in on at 0800! 

I just have one thermostat - an old Hive one. It's set to 19° and I just leave it alone. I've adjusted the Water Law as Samsung call their weather compensation. I'm very happy & my bills are very low. I think that thanks to the 5.2kW solar & Powerwall 3, the biggest part of my annual electricity bill is the standing charge!

Cheers