On Tue, 9 Sep 2008 17:25:15 +0000 (UTC), Ed Sirett
wrote:

Is this a gas, oil or solid fuel boiler?

Sorry I forgot to mention, it's oil, though I don't think Grant make
any thing else. Does it make a difference? I've never quite understood
how the air gets into the boiler "conventionally" considering the
boiler is enclosed on all four sides with enamelled sheet metal,
insulation, etc.