Potterton Netaheat 10/16 comes on OK when timer calls - fan on, pilot on, burners light. After a few minutes the system heats up and the burners go out. Fan and pilot stay on OK but burners don't relight when system cools. Desludged as much as I can with fernox and have changed pump. Appears to be an intermittent problem but is happening more and more. I turn system off and back on again, burners come back on as before but only for few mins then same problem. Any ideas

Dave G, January 2007

Perhaps Gas Aid doesn't know this boiler. If the thermostat was faulty, the fan would not run. Thermostat needs to be 'ON' for the start up to begin.

Algynon, January 2007

Looking at your question again, the pressure switch and relay must be OK otherwise your fan would shut off. If Mercury valve is OK, try your main solenoid (the one that opens the first (main) gas valve. You should normally hear it as the first 'click' in the firing up sequence. If you don't hear that click during the subsequent firing up sequences, it might be the culprit.

Algynon, January 2007

If yours is Mk1? with mercury vapour valve/switch? check out the switch is returning to the 'ON' state after the burner shuts down. Use a multimeter set to 250v and connect to each side of the switch. If it shows any reading (it will be less than 250v) after (say 10-15 seconds later) firing has shut down, then it is worn out and should be replaced. If no reading is shown (ie the switch is returned to 'ON' ) then look to the other components in the 'chain' eg solenoid or pressure switch - do same tests.

Algynon, January 2007

Although difficult to say; I personally would suggest possibly a thermostat fault within the appliance itself.

GasAid.co.uk, January 2007