I have a Lennox gas unit which must be 18 years old. Its controlled by a thermostat. Tongiht there was a very large bang followed a few minutes later by further bangs each of these bangs was accompanied by a large flame (yellow) and smell of gas where the burners are. I've turned the thermostat down so the unit is effectively off (pilot light is still on). Have you any idea what the problem could be. We are now freezing.[b][/b]
