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• Do you have a spare MCB? Could you swap the MCB with another with the same rating in the CU? The first thing I’d like to eliminate is faulty MCB.

• The next thing I’d look at is the ground-loop and it’s pump. Is the fluid level correct? Is the pump bled. Can you run the pump independently of the rest of the system?

• Now check the Capacitor. Is it swollen, leaking, or otherwise showing sign of failure? If you remove it from the HP, momentarily short the terminals with a piece of wire, then set your multimeter to measure resistance, you can expect the display to show a reading for a few seconds before returning to “open circuit”. If it only reads “open circuit” or shows a reading indefinitely the cap is dead.

• After that you’ll need an f-gas engineer to replace the compressor…

Stan wrote: ↑Thu Nov 18, 2021 8:25 am Might be showing up a faulty rcd Nowty as well as the more obvious problem.

Ken wrote: ↑Thu Nov 18, 2021 12:49 pm Yes soft start is a real pain. I have got through a few chop saws because of it. It is probably only one underated bit but for hapfarth of tar .....

nowty wrote: ↑Thu Nov 18, 2021 4:32 pm Been looking at the heat pump problem this morning.

So my RCD is working correctly and the fact that the RCD did not trip is a good sign as any shorting of the compressor windings to earth would probably be terminal.

I don't think it has a soft start.

I was not convinced about the MCB being faulty, I thought they were pretty bullet proof, however, maybe not.

Took the cover off the heatpump to see the general condition of it and still looks like almost new.

Then looked at the electronics to see the state of the starting capacitor and that looked fine but I took it out for a proper check.




I did not realise my multimeter has a capacitor function and that read almost the 50uF rating. I also checked the resistance and that started at about 25 mega ohms and was slowly rising so the capacitor is fine.



As I said in my first post, when the heat pump was running yesterday even after the first MCB trip, the water pumps were working, the temperatures were fine and the gas pressure gauges were showing normal. It also sounded normal, nothing unusual.

So I'm back to the 32A type B MCB. The heatpump is also protected by a 13A fused spur which did not blow so maybe the MCB was a bit premature on start up. Maybe its aged, or the compressor has aged and has slightly increased its start up current. Maybe I need to use a type C MCB as some websites suggest. Anyway I do have some spare 32A MCBs which are more modern than the existing one, so I replaced it for good measure.

Turned the heatpump back on and its been on twice working fine without tripping the new MCB. So either I have fixed the problem with the replacement MCB or if it happens again I'll try fitting a type C MCB, as the 13A fuse would blow anyway if there was a serious problem.

So gas boiler switched off again but used 38kWh of the dirty fuel since last night.