Right – gas engineer coming Wednesday morning (yay!). If he can fix the problem without using any parts (i.e. just by cleaning it) then it is free (yay!) but if he needs any parts, I’ll have to pay a call out charge, parts and labour (minimum £87) (boo!). He’s also going to service it and test it at the same time, for no extra charge – this is a good thing, as I have no enthusiasm for death by carbon monoxide poisoning.