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Compressor attempts start but fails - Nibe Fighter 2005 8kW

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 60 minutes ago
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 skyefarmer
(@skyefarmer)
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Joined: 4 hours ago
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Topic starter 05/07/2025 11:35 am  

Hoping someone may have seen this problem before. I have a Nibe Fighter 2005 8kw single phase heat pump which heats a swimming pool. From yesterday it is failing with the following behaviour. Starting from a full power off reset, the system waits 20 mins before attempting to start the compressor; after 20 mins I hear the compressor motor startup noise for about half a second, after which it stops; the fan continues to rotate; the system stays on, but evaporator temp, hotgas temp, etc are not right; after about 5 mins the compressor motor attempts to start again with a short pulse of noise, then stops; after the second attempt the system alarms and stops with "fan alarm" (but don't focus on "fan" because I have learnt that the alarm descriptions are pretty random).

The system had been working fine all winter (for background heating and frost protection, not pool heating) and has been heating pool fine for a few weeks this summer.

I'm on the Isle of Skye, with nearest heat pump engineers 2 hrs away, so I have looked after this heat pump myself for years: so far, 3 replaced temperature sensors and a new soft start unit (2yrs ago).

Unluckily for me this latest fault happened at 5.30 on a Friday, and the only guy who has ever helped me by phone finishes work at 5!

Any insights or advice would be gratefully received. It's been pouring with rain here for a few days so I haven't opened the heat pump lid to start poking around, see if anything looks amiss, etc.

The system is pretty old, maybe 15-18yrs, and we've had it from new.

Thanks


   
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 JamesPa
(@jamespa)
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Joined: 2 years ago
Posts: 2618
05/07/2025 12:12 pm  

I had a very similar problem with my valiant and it turned out to be a blocked filter.  Unbeknown to me I have a very fine filter in addition to the mag filter.  Heat pump engineer told me this accounts for 90 percent of call outs so definitely worth checking.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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