hot water but no heating, chaffotaeux britony 80,please help

[sonofrob]

i have a chaffotaeux and mauery britony 80 in a house i just got,,,at first the heating worked fine but no hot water,,,then the heating wouldnt work but hot water was fine,,,then yesterday the hot water was coming out the tap cold but still being heated in the boiler,,,i noticed the rads were getting luke warm even though the heating wasnt switched on,,,i fitted new diverter valve last night,,,hot water working perfect now but when you turn the tap off the boiler tries to go back into ch mode but will not fire up,,,the pump starts to run etc but it just doesnt seem to be getting the signal to fire up the burner??? any advice greatly appreciated......

 

[Gasguru]

There's an overun timer, after a DHW demand the heating may take several minutes to come back on, press reset to bypass the timer.

Have you checked the selector and temperature knobs...pull them off and check they haven't split.

Disconnect the DHW flowswitch connector and measure the resistance of the flowswitch....should be open circuit with no flow. The reed magnet inside fails keeping the boiler in DHW mode so the boiler just sits there cycling the burner on/off every so often.

Whilst you're at it do the same for the pump flow switch...when these fail ie. the reed switch sticks on the boiler can destroy itself.

 

[sonofrob]

after 3 different plumbers looking at this boiler and scratching their heads and advising me to fit a new one,,,i tried a few things myself which id read on this site,,,the problem was a blocked copper gauze filter,,,took me ten minutes with a toothbrush and the boiler is working as it should,,,saved me a small fortune..............