There isnt a short compressor, its that the operating time of the compressor is too short.  According to google it may be due to low refrigerant level or component malfunction (the other reason for compressor operating time too short is short cycling - but at 2C thats unlikley).

If Google is correct you will need a Nibe repair man

@jamespa thank you. At this stage (3rd winter with it cutting out when cold) I’m on the verge of seeing if it’s possible to replace the pump and putting a gas boiler back in. It’s costing so much money getting people to try and fix it and nothing ever seems to actually make it work properly. So disappointed 

Posted by: @fiona

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@jamespa thank you. At this stage (3rd winter with it cutting out when cold) I’m on the verge of seeing if it’s possible to replace the pump and putting a gas boiler back in. It’s costing so much money getting people to try and fix it and nothing ever seems to actually make it work properly. So disappointed 

Have you actually had a Nibe engineer in or just an installer.  You probably shouldnt be paying anything if Google is right, it should be a warranty issue, Nibe are a premium brand so its disappointing if they wont engage.  They say they will here https://www.nibe.eu/en-gb/about-nibe/contact-us

Precisely which model is this?

It could alternatively be to do with the downstream system (your radiators/UFH).  What do you have, do you have zone valves, TRVs or room thermostats, if so how are those set?  Does this ONLY happen when its 2C or below

@Fiona, James is right. The unit should still be under warranty and I'd strongly recommend contacting NIBE for them to come and check it out. If you're battling, I can contact NIBE on your behalf.

Thanks both. We’re going to contact the people who last came to look at it today and take it from there. Every time we’ve phoned NIBE in the past they just point us to accredited installers who this guy is. I think he does know how to get in touch with them though so hopefully he can sort it. This is the same alarm we get every year though when it gets cold and we’d hoped whatever the guy did last year would have fixed it so hopefully we can get some resolution this time. 

Posted by: @fiona

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Thanks both. We’re going to contact the people who last came to look at it today and take it from there. Every time we’ve phoned NIBE in the past they just point us to accredited installers who this guy is. I think he does know how to get in touch with them though so hopefully he can sort it. This is the same alarm we get every year though when it gets cold and we’d hoped whatever the guy did last year would have fixed it so hopefully we can get some resolution this time. 

If it happens only when it gets cold then it maybe that the heat pump tries to increase flow rate at lower outside temps/higher flow temps, and fails due to too much resistance.  This could be as simple as a filter blocking up which is unfortunately a maintenance item, probably roughly annually.  Why don't you find out what he does.

@editor we’ve been in correspondence with the warranty company for a year now and they told us to get a report done on the pump which we did. They didn’t agree the issues were workmanship so we got the ombudsman involved. The guy who came out last Feb did some work on the pump to get it working as well as it could. The ombudsman found that the issues could be attributed to workmanship but as we were aware that things weren’t right before our installers went into administration the warranty company don’t need to cover us. Given it has a short compressor alarm back in January we’ve contacted NIBE now to see if they can’t least look into why it keeps cutting out when cold. Now apparently as we didn’t have a survey in November (due to hoping the system could be replaced under warranty) NIBE says it’s now not covered under their warranty. I’d like to say I’m shocked but it doesn’t surprise me at all. I didn’t realise the work done last Feb wasn’t classed as a service. In addition. We literally have nowhere to go now apart from buying a new pump as recommended by the independent report done for the warranty company. I’ve been recommended to go to heat geeks but all of this costs money. I suppose we just need to suck it up and pay. This has left me with such a negative view of the heat pump industry which is a shame.

@Fiona, thanks for coming back with the update, and I’m really sorry you’re still stuck in this position. Unfortunately, what you’re describing is something we’re seeing far too often.

Before anyone here (or me) can give you meaningful help, or before I can even begin to see whether there’s anything we can push back on with NIBE, we really do need the full picture, even if it feels exhausting to go over it again.

If you can, please do lay everything in this thread. The key things that will help are:

• The exact NIBE model and size
• When it was installed and by whom (even if they’re now defunct and out of business)
• What the independent report actually concluded (especially around undersizing vs workmanship)
• The exact alarm code wording and when it occurs (outside temperature, flow temps, demand at the time)
• Whether the system has ever been serviced in the way NIBE defines a service
• Any changes made since install (emitters, insulation, controls, flow rates, buffer/volumiser, antifreeze, etc.)

At the moment, we’ve got fragments... undersizing, a compressor alarm in cold weather, warranty disputes and now NIBE declining involvement, but without seeing how all of that fits together technically, it’s impossible to say whether this is genuinely a capacity issue, a design/commissioning issue, a control fault or a protection mechanism being triggered.

And just to say this clearly: your reaction is completely understandable. Being left with nowhere to go and told to spend more money after doing everything you were advised to do would leave anyone disillusioned. You’re not wrong to feel the way you do, but before you resign yourself to replacing the unit, let’s make sure there truly is no other option.

Take your time, post the details when you’re ready and we’ll go from there.

@editor it’s a NIBE S2125-12 and was installed in March 2023 by Renewable Energy Network (now in administration).

I have attached extracts of the independent report to hide their details. The installer always ascertained the heat pump was right sized however the independent company also did a heat loss survey and they concluded the following:

We don’t think it’s ever been formally serviced, it’s had lots of visits first by REN and then one of their employees who went independent after they went into administration plus work done by the independent company who did the report but we don’t think any of those were classed as a service. 

By way of update, NIBE have said they will send someone to do a service for £335 I think it is. We are not sure whether or not this will sort the issue of it tending to cut out when cold outside or not. We know if won’t sort the other issues such d the pump potentially being undersized.

Hope this helps. 

Thanks 

Firstly Im very sorry to hear about your problems. 

Posted by: @fiona

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We don’t think it’s ever been formally serviced, it’s had lots of visits first by REN and then one of their employees who went independent after they went into administration plus work done by the independent company who did the report but we don’t think any of those were classed as a service. 

Did you get an insurance backed guarantee for the installation (you refer to the warranty company so I presume so), the whole purpose of this is to deal with the situation where the installer goes into administration.  Such a guarantee is independent of the manufacturers guarantee.  The manufacturers guarantee covers the product (the heat pump) only and wouldn't, for example, cover it being undersized as that is not a heat pump product fault its a system design fault which is the responsibility of the installer and is therefore hopefully covered by the insurance backed guarantee. 

Alternatively if you paid anything on credit card section 75 may come into effect, making the Credit card company at least in part liable.  

Posted by: @fiona

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So at -3 for example, a 12kW Nibe would only actually give you 8kW output, which would explain why the heat pump is struggling to perform during the colder months of the year when the temperatures are very low. 

Im surprised the drop off is as much as that but if it is and your heat loss is 12kW then it is well undersized and can be expected to perform adequately only when the temperature is above about 4C.

Posted by: @fiona

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By way of update, NIBE have said they will send someone to do a service for £335 I think it is. We are not sure whether or not this will sort the issue of it tending to cut out when cold outside or not. We know if won’t sort the other issues such d the pump potentially being undersized.

A service of the heat pump wont fix undersizing nor several of the other issues identified in the report which are workmanship of parts other than the heat pump itself.  This would, to my mind, potentially be a waste of money given what you have said above.

I'm left wondering why the insurance backed guarantee doesn't cover the problems you have, including replacing the heat pump for one of the correct capacity.  You would need to post both the full report (with only personal details and address redacted) and the guarantee itself for me to comment further on this, but @mars may have the information already.

@jamespa the insurance backed guarantee who we’ve been fighting with for a year won’t cover us as we were aware there were problems before the installers went into administration. They aren’t really worth the paper they’re written on and another reason I’m trying to highlight pitfalls as you think having this workmanship warranty covers you! 
No we didn’t pay on credit card. I’m not actually sure we were given that as an option.

thanks