On 20/12/2017 12:06, John Rumm wrote:
On 20/12/2017 10:32, wrote:
On Tuesday, 19 December 2017 17:44:05 UTC, Steve PoultonÂ* wrote:
Please help. I have a basic understanding of electirics, but 5
Electricians
are stumped and I don't know where to go next.
for full context, visit
https://www.homeownershub.com/uk-diy...t-1257719-.htm


There's even more context at

https://www.electriciansforums.co.uk...ircuit.124737/


So far possibilities seem to be (a) a polarity error as I suggested -
possibly introduced due to a meter change - or old 15A MCBs
overheating and thermal tripping.

The polarity error is possible, but it seems hard to believe that none
of the visiting sparks have done a continuity test between L+N and E on
the circuit and the heater (even if they did not do a full insulation
resistance test).


I don't think it is a polarity error, it has to be thermal operation of
the E7 board oldish MCB(s). Try replacing the MCB for the heater circuit
that is tripping.