Hi Stephen, thank you for your reply. I have cleaned the boiler. It is quite old and very dirty. Just moved in to this place. I'm not sure if the pressure is adjusted correctly. The pressure screw seems to be adjusted out ,anti clockwise. One more turn and it might fall out. It takes a while to ignite and then stops heating after about 40 minutes.No more heat after this. Sorry for being so vague, it must be hard to comment on something you cant see.