In article ,
John wrote:

I'd suggest the most likely scenario would be either incorrectly shut door
as you suggest or a bit of cinder had become trapped in the air intake, if
its a natural draught unit, so the thermostat couldn't close the flap to
slow the burn when the boiler got hot.

It's not natural draft - it has a fan that blows to fan the fire. I guess
there is just enough of a vent somewhere that it slowly smolders for days
if heat isn't needed.

I've checked with the dogsitter again and it is apparantly working fine
so I think the door not shut properly idea is favourite. She can't remember
if the fan was actually running or not.


Result the boiler would actually boil
projecting steam into the F&E tank, melting the ball and causing the mayhem
you describe. It is a good idea to use a metal (copper) float on an F&E tank
for just this reason.

just popped in wickes to grab a new valve and ball. They don't do anything
other than plastic Proper plumbers merchant for that I guess (or maybe
BnQ whorehouse I suppose)

In either of the above cause options opening and closing the offending item
may clear the problem.

Yeah.

Of course you could be on the way to a failed thermostat but this doesnt
usually cure itself

As I said, it didn't strike me as sounding like a failed thermostat as it
seemed to cure itself. I'll go with not shutting the fire door properly
as the problem I think.

Thanks for confirming my thoughts,

Darren