On 12/01/2017 12:04, mechanic wrote:
On Wed, 11 Jan 2017 22:54:38 +0000, John Rumm wrote:

Which is why many modern designs run the case at negative pressure
- so if there is a leak it draws air in, rather than allows
combustion products out.

Can't see any mention of this on the Vaillant or Bosch sites?

On my Vaillant, the fan's induction side is connected to a duct that
stops open ended inside the case. The case is open to the the outer part
of the concentric flue - but the duct is not attached directly to the
inlet. So the fan is actually drawing its combustion air from inside the
case, and that in turn will pull air in through the balanced flue. I
believe this type of design is fairly common these days.


--
Cheers,

John.

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