On 03/02/2020 08:48, Ray wrote:
"Adrian Brentnall" wrote in message
...

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?

Some can do.

Thanks - that's what I was reading on the 'net


Am I seeing an MCB failure, rather than a heatpump failure?

Only way to be sure is measure its power use or
swap the MCB and see if that fixes the problem.

I know that the 'running' current for the heatpump is around the 10 -
13A range, but I remember that a standard 20A MCB would trip out on the
initial switch-on current, when the compressor starts - which is why
they fitted a type 'D' - 'slow-blow' MCB in the first place.


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

No way to say for sure without measuring or swapping the MCB

Yes - I think MCB-swapping is a good place to start.
Now just got to find a supplier that has some in stock.
Thanks
Adrian