Hey all, 

I just wanted to put in an update and again ask for some advice. 

I got my radiators changed upstairs to a bigger size - thinking that was the issue.  

Mitsubishi engineer came out in May. He found several flaws with the installation but did not hand me to have the report as I did not pay for it. The developer paid for the callout. He fixed some pump attached to the cylinder. The night he came he got the heating working full blast upstairs and the heat pump stopped making the high pitched noise. The second day, things were back to where they were. No heating upstairs, high consumption ( COP of 3 at very very best with super hot weather), horrible noise coming from heat pump etc.

After another 2 months of calls and emails, I decided to log in a complaint with NHBC and call my solicitor. The developer then rang me and said he has no clue what to do / how to repair it and he does not understand what mitsubishi is suggesting. He said he only installed the heat pump as he was building the house for himself and he was advised it is the best option, but his gas engineers have no experience with renewable enenergy. He is willing to swap my heat pump for a gas boiler....

Well isn't that going backwards and sideways? Seems like a waste, but then again it is not working as it should and I am very panicked like in game of thrones that winter is coming and I will have an 11 months old freezing in his bed and pay about £500 /week for this scenario. 

I am reluctant to keep the heat pump, simply because the Mitsubishi Engineer that came made a comment about the high pitched noise " i've never heard one so loud. I have updated the system, but I was advised by techical team that if the noise comes back, then the unit needs changing". 

Heat pump is out of warranty ( explanation is somewhere in my posts above). So I will be out of pocked by a lot if I want to keep it and get everything fixed / changed .  I assume a new pump plus fixing is around 10k, even after grant?) . Developer is reluctant to do that as he said he can't fix it if anything was to go wrong as his people are unexperienced .He will sort out a gas boiler . 

What do you guys think? what would you do? get the gas boiler if you were in my shoes?Take into account  I have no money spare as I just bought the house and have a newborn, so can't really be spending what I do not have... 

Many thanks, 

Anca

@anca1808 

It's a shame to say it but if I were in your position under your circumstances I would snap his arm off for the gas boiler option.

Posted by: @morgan

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@anca1808 

It's a shame to say it but if I were in your position under your circumstances I would snap his arm off for the gas boiler option.

Hmm

Before doing that I would want to be certain that there are no attendant liabilities related eg to planning permission or grants that the developer, who may not know about them, will foist on you and also I'd want to be certain that the problem is the heat source not the rest of the system.  If the rest of the system is at fault changing the heat source isn't going to fix it.

Something about liabilities and warranties isn't making sense and so I'm suspicious you don't have the whole picture.  What is the developers motivation, why is he offering anything if he doesn't have to?  And if he does have to then is he just trying to get you off his back whilst dodging other issues which will come back to bite later. 

I presume incidentally that there is a gas supply to the house so his offer is practical without you having to pay for a connection 

@anca1808 I have just reviewed the whole thread.

In summary it seems

you have several issues (undersized rads, inadequate insulation) which have been identified and fixed, albeit not yet tested because it's too warm.

The high pitched noise, if it's coming from the outdoor unit, is a problem with the outdoor unit.  The fact it's out of warranty is not your problem, it's a problem for the developer who sold you a brand new house which should work.  Whatever mitsubishi need to do to fix that, he should pay for, even if that means a new unit (which is about 4k retail not 10k btw, like for like swap, small change for a developer).  Actually heat pumps are basically assembled from pretty simple components so more likely it's a component swap.  One thought about this, could you check the top is level in both directions.  Out of level heat pumps cause failed fan bearings which can certainly result in a high pitched noise!

Also you say that the mitsi engineer identified several faults with the installation, have these been fixed?

Although not proven, it's highly likely your heat pump is well oversized based on your epc and house area.  This will reduce efficiency although it's difficult to say by how much.  That said if you can exploit this, maybe with the help of havenwise or homely, to take advantage of your tariff it may not be a problem and could even be an advantage.

It's impossible to tell from the posts whether the efficiency/consumption has improved or not because you didn't say much about what happened after the insulation was done.

I'm not sure whether you ever did the esential optimization job of turning all the trvs and thermostats to max and then adjusting the weather compensation curve down until the house is just at the right temperature with the heat pump heating 24*7.  This is fundamental and, until this is done, you really can't judge efficiency 

I think you switched to octopus cosy.  This tariff works well only if you adapt the way you use your high consumption electric appliances to avoid the peak hours and tweak your heat pump programming likewise (which is not straightforward).   If you don't do this then it quite possible you won't benefit or even that it will cost you more.  Because it's quite a complex tariff this isn't particularly easy to do unless you use a service like havenwise (only £50 per year and you get a free trial period I believe) to automate it for the heat pump, and are disciplined about when you cook, do washing and use a dishwasher if you have one.

Personally I wouldn't give up yet, if you can get the heat pump working efficiently, and there is no reason why you shouldn't, you will end up with a more comfortable,  house than one heated by a cheap gas boiler operating at a constant high flow temperature (which is what you will get), for a similar running cost.  And of course it's more climate friendly) However to do this will probably require a bit more systematic work on your part which people on this forum can help with.  I think most of the mysteries are now solved, so it should be pretty straightforward if approached systematically.

If you do decide to accept the offer of swapping for a gas boiler, I still recommend you take heed of my post above.  The developer is making you an offer to benefit him, not necessarily to benefit you!  

My final comment is do what's right for you, not what's right for others, including me, who, whilst they may be giving good technical information , are in different personal situations with different priorities.

Hi James ,

Yes. There were multiple issue.

Insulation was solved 80 %. Radiators were changed to bigger size. But even with that the upstairs never got hotter than 19 20 degrees , nor did the radiators and it was mostly because the heat from downstaira was travelling up. 

The mitsubishi engineer came for a diagnosis and check up as he was not pay for fixing anything. He did fix something regarding the cylinder and like I said whils he was there he got the radiators upstairs really warm and they worked until temp reached what is was sat, but next day they did not worl anymore....

I ran on weather compensation since march, I had everything on all time , adjusting the curve in cold days , but with upstairs not getting warm , only the warmth that was travelling from downstairs. So my issue is more complex than just performance. I started at 1.6 probably COP and got to at very best to 2.8  with warm weather. Imagine with outside 25degrees plus , the heat pump is still consuming around 15kwh/ day...on what...f*** knows. 

I changed from Octapus cosy as , as you said, it was hard to do all electricity consuming jobs off peak times . So I am on a standard fixed tarrif which works very well for me   but cost is stil high sue to the silly consumption of heat pump.

I know not having warranty is not my issue. I bought a new build that was build in 2022/2023, but was only signed as completed when i bought it in feb 2025. So the developer has to fix my heating issue. Why is he not wanting to solve my heat pump? i do not know, but i have 10 years warranty on house and insurance , so even in the next year and a half he still needs to fix my heating if it is not working.

I do have a gas source as I use a gas hob. It won t be cheap for him to connect and put a gas boiler as the gas meter  is on other size of house and i will refuse putting a pipe around full house or under the floors of house aa I just finished flooring/ decorating almost 70%. I am guessing the developer might want to switch to gas , as he has people on the books for 20£/h to repair gas boilers. Whilst if my heat pump break again he is out of pocket by a lot, as a heat geek charges around 90£ /h just for assessment ( as I called a couple) . 

All in all, I am super dissapointed as I though I will be better off with a property that is so green with ASHP and l had nothing but issues. 

Many thanks to all for the advice and information. 

A 

From what you say about the radiators upstairs it does sound like you have problems with the pipework etc (which may be as simple as balancing or even just air in the system since it did work for a while).  The Mitsubishi engineer likely wont fix those and may not even diagnose them because its outside his area of expertise.  Furthermore its quite possible that a gas boiler wont fix it either!  What you need is a competent heat pump installer/heating engineer/plumber who can take a system view not just the view of the heating source.  The fact that the rads aren't heating the upstairs will seriously compromise efficiency because it means that you are having to run at a higher flow temperature than you would if all emitters were working properly.

In terms of tarrif options I have 7hrs cheap at night which is manageable in terms of complexity but still gives the opportunity to game the system a bit.  Something like Havenwise or Homley is a very good option to optimise and reduce the complexity when you have a ToU tarrif, although I haven't bothered so far because of the simplicity of my tarrif, but if I were choosing Agile or Cosy I think I would.

Presumably you went through a period when the heating was off altogether and only DHW was being heated, how much were you consuming then?

Really this comes down to either accepting the offer of a gas boiler (but noting carefully that the heat source is clearly NOT the only problem)  or insisting the developer sort it out by getting the right person on the job to diagnose and report.  IMHO this is not the Mitsubishi engineer alone, because it needs a system view not a component view.  Furthermore they need to be someone who understands heating systems, not just someone on £20 ph who can paint by numbers.  The obvious choice would be a 'Heat Geek' but @mars may be able to recommend someone else in your area. 

Alternatively you could try (a) drawing a diagram of the system as best you can and (b) carrying out some systematic diagnostic checks suggested by those on the forum, and very likely someone will work it out.    Without actually seeing it its quite difficult to ask the right questions, so this isn't the best and anyway its really for the developer to do.  Nevertheless if you want to attempt this I'm happy to try to help so long as you can take some measurements and make some observations in response to questions. 

PS to above.  I just looked again at the photo you posted very early on.  Are the feed and return from/to the heat pump really disappearing into the floor uninsulated?  That's certainly what it looks like.  If so how long is the underground run and what do you see where it emerges the other end?

@jamespa 

Hi James , 

I have just spoken to the developer. He admitted that the installation might not have been done properly 3 years ago, but the person who did it has left the company. He said he does not want to repair it as he has no one competent to do it , he must get a third party and as if it breaks again, he has no people employed that can fix it ( as I suspected) . Although that is not my problem i fear that if I do insist for it to be fixed i will end up waiting months for something to be fixed. 

I will go for the gas boiler simply because i want somesort of heating in the winter and not to spend all my money on mortgage and energy bill. 

He also said that if there is a problem pass the gas boiler he will fix it , but I guess he thinks that if the boiler is running at higher temperature, that will fix the heating problem (?!) . 

All of this comes from his solicitor which to me does not sound like the sharpest tool in the box . But I am fed up because I documented myself so much on heat pumps , installations , optimising my system...but without someone on the other end to discuss it with, it is pointless. they did not even know how to look on the setting at the main console. 

Unfortunately I am a bit constrained by money and time ( and surrounded by incompetent evaluators of the heating system/ASHP) and have to go along with the boiler change..

And yes, those pipes are UNINSULATED and they run about 4 feet into concrete in the garage ...i know...ridculous. . I had weeks of arguments about my insulation as the house was signed completed which meant it is all proper and I argued so much it was not !

I am.accepting the fact that I am one of those unlucky people who buy a newbuild and have a nightmare ....

Many thanks tp all for the advice and effort into explanations. 

A

Posted by: @anca1808

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And yes, those pipes are UNINSULATED and they run about 4 feet into concrete in the garage ...i know...ridculous. . I had weeks of arguments about my insulation as the house was signed completed which meant it is all proper and I argued so much it was not !

Well at least that solves the mystery of where the excess energy is going, straight into the ground.  It doesn't account for a poor COP though.  Those pipes must not be reused under any circumstances (you shouldn't bury copper pipes directly in concrete anyway, it rots them).

Posted by: @anca1808

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I will go for the gas boiler simply because i want somesort of heating in the winter and not to spend all my money on mortgage and energy bill. 

He also said that if there is a problem pass the gas boiler he will fix it , but I guess he thinks that if the boiler is running at higher temperature, that will fix the heating problem (?!) .

Possibly, if you throw enough energy at it at a high enough temperature you can overcome many problems, but it will need a mixing valve/manifold for the UFH - without one your flooring will be ruined and it may even be too hot to walk on.  Please make sure he doesnt bodge this also

Posted by: @anca1808

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I am.accepting the fact that I am one of those unlucky people who buy a newbuild and have a nightmare ....

 

Im sorry to hear that but many builders are a pretty scummy and frankly incompetent lot.  There are of course good ones also.

Good luck