The flue exits into the chimney which is covered over so that nothing can get into it.
Eh? That's a bit ambiguous.
I thought these all had fans - you'd hear as soon as the boiler is told to "go", even before the flames light.
These boilers (if like the thorn apollo) do tend to make banging noises on "high" because they're mostly a bit scaled up now, and they overheat fairly readily. The thermostats aren't the most reliable but aren't very expensive (~ several pounds each).
Also the thermocouple is sometimes replaced with a non-"interrupter" one, which effectively disables the overheat thermostat - not a good idea!
I'd recommend you do get it looked at, checking that the thermostats are present and working, and the "chimney" is ok! Why it failed to start the other day remains a mystery, could be the gas valve decided to stick?
Recently went to an apollo which had been making awful noises and sometimes cutting out for 2 years, then finally there was no heat so it was switched off. Tenant had no CH for
2 more years, landlord got him to buy an electric heater which he moved about! When I got a call it was because the cast iron loo cistern had broken, and the guy had been using a bucket to flush it for 3 months before telling the landlord. Got someone else to do the loo, but asked about the CH. Landlord had though it was just one radiator not working properly and was livid when told the situation - told me to fix it, new boiler or whatever it took.
Changed the pump and his apollo is running as quiet as a mouse - that, plus a bit of balancing, is all it ever was. Tenant says I can call in for tea any time I'm passing!
