On 03/01/2021 14:06, Dave Liquorice wrote:
On Sun, 3 Jan 2021 12:56:56 +0000, Roger Mills wrote:

Unless the boiler is in an unheated outhouse or attic, why would that be
any more likely to freeze than the pipes?

Boiler has balanced flue that could allow cold external air to
circulate through the heat exchnager.


Why would it do that without the fan running? "Balanced" means equal
input and output pressures.
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Cheers,
Roger