Mr R called me from before Christmas. He has a flat in Northampton town centre and he said his Electramate had stopped working again. He called me because I had previously repaired it back in 2017. I checked with him the basics on the phone and established both the radiators and the hot water had failed. So I asked him to look at the electricity consumer unit in the hall cupboard and check none on the circuit breakers was tripped. All looked correct so I explained my current charges and arranged to visit the next day.
On arrival I re-checked the consumer unit myself, noted the pressure gauge on the front of the appliance read 1.0bar (the correct value), then I removed the front cover. These appliances look really complex inside but the fault was immediately clear, the lower of the two overheat protection thermostats was tripped, indicating the ‘flow boiler’ had overheated. Pressing the ‘re-set’ button on the overheat protection thermostat brought the unit back to life. That however, is not all that needs to be done when an overheat protection device has tripped - the cause of the trip needs to be investigated and found.
In this case, some testing with my multimeter revealed that one of the three power relays (these supply power to the three heater elements) was stuck/ammed in the ON position. This meant that when the unit reached correct temperature and the control board withdrew energising voltage from the three heaters, one heater remained ON and still heating. This explained why the flow boiler overheat protection safety thermostat has tripped.
I fitted a new power relay from stock in the van and tested the new relay for correct operation. I checked the radiators and the hot water were working now as expected, and left Mr R with a working Electramate in time for a warm Christmas.
Copyright Michael Bryant 2020
Site first created 31st December 2006
Last updated 2nd February 2020
Gas Safe Register 197499, CIPHE registration number 56207