pulsa coil A-class thermal store water boiling!!

I was called to investigate steam coming from the vent pipe!

The pcb display was showing power/calling for the off peak heater, I noticed that there was 240 volts being supplied to the off peak during the day, I can only assume that the consumer unit isn't dual supply (econmey 7)
On carrying out some tests, both s3 and s4 thermisters seem to have a steady resistance reading.

Could this be relay R2 (off peak) shorting out?

Thanks
Allan

Could be sensors 1 or more of 3.
Fault codes checked?
Relay needs checking.
Off peak should not be on in the day unless E10 perhaps.
Mike
MGC/H2O
Norfolk

I think it is an E10 supply, this would explain the power supply.
I didn't see any signs of lock out or other fault codes, that's not to say there wasn't any as I my not be reading it correctly.

Could the relay R2 be faulty? It could be getting stuck in the on position, then causing the unit to over heat? This would also point to the over heat stat being faulty as it doesn't cut the power supply to the heater, causing the boiling of the thermal store?

Your help is greatly appreciated,

Thank you Mike

Regards
Allan

Swop the relays over.
And if you need to test the unit.
Put a supply to it.
Mike
MGC/H2O
Norfolk

I'll give that a try and let you know!

Thanks Mike

Allan

Yep I agree with Mike. A relay has jammed in the ON position. Strangely there is no separate overheat protection on the A-Class

Mike