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Compressor attempts start but fails - Nibe Fighter 2005 8kW

Air Source Heat Pumps (ASHPs)

Last Post by Mars 1 month ago

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skyefarmer

(@skyefarmer)

Active Member Member

Joined: 2 months ago

Posts: 6

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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Posts: 2719

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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skyefarmer

(@skyefarmer)

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Posts: 6

Topic starter 05/07/2025 12:38 pm

@jamespa Thank you! As soon as it stops raining I will check that out. Looking at manual now.

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JamesPa

(@jamespa)

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Joined: 2 years ago

Posts: 2719

05/07/2025 2:24 pm

It might not be in the manual, mine was a rather innocuous third party 40mmx80mm brass fitting between the heat pump isolation valve and the heat pump itself, on the return.

It may of course be something completely different. Any fault codes?

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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Mars

(@editor)

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Posts: 3390

05/07/2025 2:39 pm

Posted by: @jamespa

↑

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.

That's a very good suggestion. I'd forgotten that we had a similar issue a couple of years ago, but ours was accompanied with an error on the screen that I translated into a flow error. Given the age of @skyefarmer's system, I'm not sure the control panel throws up error codes. @skyefarmer do you have any errors?

In closing, that is probably the best name for a heat pump to date. "What heat pump do you have?" The "Fighter". Terrific name!

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skyefarmer

(@skyefarmer)

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Posts: 6

Topic starter 05/07/2025 2:43 pm

Update: It finally stopped raining and I opened up the heat pump. The attached picture tells the story. Quite surprised that can happen!

So I'm currently searching for an appropriate replacement capacitor for the Ducati energia 16.33.5660

I usually use RS Components, but not looking good. Does anyone know what the modern equivalent is? Thanks. Will let you know if I find it.

Update 2: I've ordered a Ducati Energia 4.16.33.56.60 from TME Electronic Components. Fingers crossed for the new one fitting and me being able to salvage the wiring.

This post was modified 1 month ago 3 times by skyefarmer

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JamesPa

(@jamespa)

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05/07/2025 3:59 pm

@skyefarmer pleased you found it!

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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Mars

(@editor)

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Joined: 5 years ago

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06/07/2025 7:42 am

@skyefarmer great you located the source of the issue and that you have the skills to replace the capacitor. Fingers crossed!

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Scalextrix

(@scalextrix)

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Joined: 11 months ago

Posts: 53

06/07/2025 2:50 pm

Posted by: @skyefarmer

↑

The attached picture tells the story.

"To tell you the truth, I don't know if HAL is homicidal, suicidal, neurotic, psychotic, or just plain broken."

I think we know which category yours falls into @skyefarmer

Good luck getting it fixed.

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skyefarmer

(@skyefarmer)

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Joined: 2 months ago

Posts: 6

Topic starter 19/07/2025 8:20 am

Update: All fixed. Replacement Ducati capacitor is in. The only delay was getting hold of some stranded copper wire of suitable diameter to handle the start up current (approx 16A).

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Mars

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