I'm not suggesting we will take chances - if there's a prob, it will be looked at by experts - 
Agreed - but you can put some water pressure in there and see if anything obvious happens. A bit of diagnosis and going armed with a few ideas will save you a fortune when you get someone in - because if you appear clueless they will spend ages doing unrelated stuff at 50 quid per half hour. Just like when you take your car to a main dealer. Been there, done that.
Look for signs of leakage. Anything under the boiler or any of the rads? Next, there should be a pressure relief valve that discharges excess pressure outside the house. Go and look at the outlet and see if it's got wet.
Then put a bit of pressure in the system and see if there's leakage from somewhere. Could be a number of issues:
Catastrophic failure of the heat exchanger in the boiler - odd that it works on hot water though.
Leakage from a rad or something else in the system.
Leakage from the pressure relief valve
Failure of the boiler thermostat so the water has boiled, overpressurised and forced its' way out of the relief valve.
Is the boiler a room sealed type with a fan assised flue? If so, the boiler should be contained in a sealed box that can't let CO out into the house. There would have to be obvious leakage or damage to the case for this to happen.
If it's not room sealed, it relies on airflow through the flue or up the chimney by convection, and a blockage could cause it to vent into the room. In this case, get a technician in to check the flue. They will normally do this by lighting a pellet of smoke generating material by the burner and making sure the flue carries it all away outside the house.
Just a few pointers, so when you get told the equivalent of "head gasket, mate" you are pre-armed!
As others have said, CO is deadly, so don't run the boiler without ventilating the place or when anyone's asleep until it has been checked.
Kevin
Author
Topic: Combi Boiler Problem (Read 2237 times)