I have a Bryant furnace. When the furnace is started manually with the thermostat, the gas builds up to the point that when the ignitor sparks, it causes a very loud bang and flame shoots out from the front of the furnace. The service man who cleans the furnace yearly says it is no big deal, that it is just a build up in the cross over from the prior year, how ever, I have people who have never had their furnace cleaned for years and they dont have this problem. The bang shakes the house and scares everyone to death. Does anybody know if the information the service man is giving us is accurate or should we really be concerned? Thanks for any tips.