Smell of gas from flue

[jimrat]

Tonight I came home to a cold house- when I checked the central heating (Potterton Prima F) the timer was calling for heating and hot water, and the exhaust fan was running, but the flame was extinguished. When I checked outside, there was a strong smell of gas coming from the flue. I turned the unit off at the wall, then powered it up again, and it struggled to light- it ran the purge cycle 5-10 times. I went outside and put my had over the flue vent and it fired up straight away.

The boiler has been running ok, but I have noticed that sometimes it runs the purge cycle several times before the flame igites.

If the flame extinguishes, surely the boiler should detect this and cut off the gas? Could the flame be blown out on a windy day by air travelling down the flue- it is situated 7ft above the ground on a side wall.

Presumably this needs urgent attention!!

 

[kevplumb]

big style turn it off and get a corgi in quick

 

[ChrisR]

Could the flame be blown out on a windy day by air travelling down the flue

No!! It's a balanced flue so the wind goes against both ends at once.

Your boiler is wot we call Immediately Dangerous. It might be going for a walk any time - with its favourite wall.

 

[jimrat]

OK, boiler turned off at the wall!! Anyone got any ideas as to what is causing this?

When I smelt gas, the boiler wasn't in its purge cycle. That says to me that the flame must have extinguished for some reason, rather than not lighting in the first place. Could this be a dodgy flame-sensing thermocouple? Dont these things fail safe?

 

[kevplumb]

the thrmocouple should lock the gas valve off if it does not sense the flame

could be an undersize gas supply starving the pilot when the main burner is trying to light

 

[ollski]

There is a white wire from the pcb to the gas valve, if it has a path to earth anywhere along the lead the gas valve will open as soon as it gets a call for heat before the pilot ignites.It does this straight after every purge cycle.