Sounds like a small heat pump what does it actually achieve?
Brian

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"Adrian Brentnall" wrote in message
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On 03/02/2020 18:55, ARW wrote:
On 03/02/2020 08:24, Adrian Brentnall wrote:
HI Folks

Our domestic central heating is run by a ground-source water heatpump -
most of the time this is very successful, it was installed about 12
years ago.

In the last 24 hours, the MCB that feeds the heatpump circuit has been
tripping out. When it's manually reset, the heatpump fires up again and
runs.. until it trips out again.

Wiring is as follows
Main CU has a D40 MCB that feeds a smaller CU in the workshop, where the
heatpump is housed. A D20 MCB in this smaller CU feeds the heatpump -
which is nominally 3kw, but takes a big switch-on current.

As I say, this has all worked well for the past 12 years - until last
night.

So - do MCBs age over time? Am I seeing an MCB failure, rather than a
heatpump failure?


I have a call into the local engineers anyway - but just wondering...
I'd rather replace an MCB than a heatpump!



I would expect ageing to occur faster if held close to the maximum
current for long periods or in an overheated CU ie between two heavily
loaded MCBs.

What's the MCB you require? There might be one on the shelf at work and
if there is one you can have it almost free if you want it - P&P costs
must be donated to charity....


That's very kind of you Adam - but the narrative has moved on from this
morning..

Drove to the wholesaler in the next-town-but-one - collected a couple of
D20 single-pole MCB's.
Got back home, all cocky, like - installed a new MCB and the darn thing
wouldn't run for more than a few minutes.
In fairness, wholesaler fellow said it was quite possible that the MCB
could have been the problem - it just wasn't..

Decided to apply a bit of science (perhaps a bit late!) and measured the
current into the heatpump at 35A (!) - which would explain why the MCB was
tripping.. - should have been nearer 13A.

Contacted the heatpump guys, under instruction from them checked the
current to the 'motor run' capacitor - which was 9/10 of sod-all.. and
should have been somewhere in the 6A range.
Other diagnostic was that the compressor sounded to be running a bit
'rough'.

Drove back to the next town and collected a new 50ufd / 400v motor run
capacitor from the heatpump guys. Swapped it in, and the meter showed 6A
through the capacitor and 12 - 13A to the entire unit.

Problem seems to be solved..
Heat-pump supplier pleased that it's fixed, regretful that he can't sell
me a new compressor!

Thanks everybody - and particular thanks to Adam for the generous offer...