If there's a leak between burner and flue, it will just blow the higher pressure case air into the flue, bypassing the burner. If it's so bad as to cause the burner to produce CO, it will be ejected out of the flue, but couldn't even get back into the boiler casing, never mind the room. If the boiler has a pressure test as part of the ignition sequence, a leak that bad would cause the pressure test to fail and abort the ignition sequence.
I'm not sure which particular boiler you have in mind but if the fan in my Baxi Solo were in the inlet rather than the outlet - so that the combustion chamber was at a positive pressure relative to the room - and if there were a leak in the rope seal at the front of the chamber, some of the products of combustion would get into the room rather than going through the heat exchanger and out of the flue.
Yes, I did both!
I got the bloke who originally installed it to have a look at it. He took the combustion chamber to bits and cleaned it out. There was a bit of rusty crud in there, but nothing untoward - and no soot build-up or anything. The only obvious problem was that some of the lower 'fingers' on the centre sections of the two baffles which fit between the three sections of the heat exchanger (No. 39 on the picture at
Clearly, it would be desirable to fit new baffles but, according the Baxi site, they're no longer available. I can't help feeling that there will be some lurking on somebody's shelf somewhere or other - if only I knew where to find them. Do any of you have any contacts who stockpile obsolete boiler parts? FWIW, the Baxi Part Number is 226421, and the Gas Council Number is 364 794.
Even _above_ burner level it's only pressurised fresh air next to the case. I meant it about the combustion chamber and heat exchanger being _entirely_ surrounded. The fact that the casing runs cold is a dead giveaway!
It could choke itself with a leak on the suction side of the fan into the exhaust - it would suck exhaust into the intake.
But it does have a pressure switch.
Andy
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