My bro has a Ravenheat boiler which takes a few minutes to fire wether it be on ch or hw mode? When turned on it goes through all the motions of lighting i.e fan running etc but just doesn't light? it'll do this a few times then eventually it will fire (sometimes taking up to 5 mins to light). Once it has fired it's ok and will stay lit. I was told this may be the thermister but if this was the case wouldn't it be either ch OR hw rather than both? Is it more likely to be the pilot burner? any help appreciated! Thanks, Kristian. [/i]