In message , YAPH
writes
On Sun, 17 Apr 2011 22:07:46 +0100, Steve Walker wrote:

I don't know about this particular boiler, but I've often wondered
whether there is any great risk to poor combustion with most boilers
these days, as they are generally room sealed and under negative
pressure due to the exhaust fan, therefore they should be unable to leak
CO into the room.

It's not as dangerous as with a non-room-sealed type but it's still
putting CO into the atmosphere outside which can - given
prevailing wind conditions - get back into the house. Or a neighbours'
house.

The soot also progressively clogs the vanes of the heat exchanger

--
geoff