We have an ongoing problem with our heating system which many visits from British Gas have failed to solve. Our system is a condensing boiler which we had fitted over 10 years ago, keeping most of the the original pipework and water cylinder. We regularly bleed air from radiators and other valves in the pipework, but within a few days the air is back again. The latest theory from British Gas was that air was getting in through the header tank so they converted it to a closed system, but the problem persists. There cannot be an appreciable leak in the system as the pressure very rarely needs topping up.
We have a theory that I would like to run past any experts on here to see if it may be feasible. If there was a leak in the coil in the water cylinder, is it possible that when the water level drops air could be introduced into the heating system? More air does seem to be getting into the system when we have used a lot of hot water, particularly when the changeover valve is on heating only.
Thanks in advance :-)