Got a problematic Potterton Netaheat 10-16 boiler. It will only light when it's been off for half an hour or so. When I start it from cold, the pilot lights after about ten seconds and then the main burners come on about 40 seconds later. This is all as per the manual
However, when the thermostat cuts in (i.e. turns off the gas flow), the boiler will not relight [1] until it's been turned off (at the wall switch) for a while. Even if it's cold (i.e. hours have passed since the main burners were running) it still seems to need turning off at the wall switch for at least five minutes.
Any ideas here? The service bloke seems to think the thermostat is at fault. The neighbour's suggested the mercury vapour switch. I think she might have more Clue than the Corgi-reg'd service engineer...
[1] at this stage the pilot light is off.