biasi boiling switching on and off

ID guess its the air pressure switch or something to do with th venturi for the air pressure switch

its just a guess min

-- gastec

p.s. also check to ensure that the flue is still connected correctl

-- gastec

I'd also hazard marginal flame detection (removing the cover alters the flame position slightly in it's favour.)

The OP should note that leaving the cover off is not a good idea (even though you can get the thing to work) as the boiler is no longer room sealed. In some cases, the flames, on startup, don't always go where they should there is a distinct possibility they could catch something nearby...

Ive done a bit more investigating and found that if i open the littl

cap on the top right hand side of boiler it seems to work.soon as close it it shuts down and comes back on. This pipe goes to the bi vent pipe.if i open it i suppose it lets the air in to the room. flu pipe seems fine. is there a list of things i can follow

-- bbuk

what is the Gas Council Number of your boiler

I still think its something to do with your air pressure switch or th venturi at the fan/ the rubber hoses to the air pressure switc should give a differential pressure in excess of 2mbar...see you instruction book for exact pressur

-- gastec

how do i check the switch, i'll have to get the number tommorow

-- bbuk

a standard U gauge ......TURN GAS OFF

remove air pipes from fan....attach u gauge across the possitive an negative ports that the air pipes were connected too.... turn on boiler .....record pressure dif

-- gastec

I'm really guessing here and if you have a camera putting a few pictures on the net would really help a lot.

I think you may have opened a sampling point for the flue gas analyser. Allowing flue gases to escape into the air inside (not a good idea) has slightly increased the air flow rate enough to get the APS to switch.

This would also explain the original symptom - the air flow reduces very slightly through a hot boiler.

My money would be on the following in more or less descending order of likelihood (IMHO).

It's all educated guesses. NB Some (crappy) models have fragile plastic ends of the APS tubes in the flue and these break and crumble. You have been warned.