I have a baxi 80e convi boiler. I have just had it powerflushed and had no problems before. But now when I use the hot water and turn the tap off, I get a loud banging/knocking noise almost like a release of pressure. This does not happen when the central heating mode is on and when the tap is turned off the boiler flicks into the central heating mode. Could this be that the powerflushing has pushed scale and/or sludge into the heat exchanger and that the powerflush was not carried out correctly?
I think you will find most combi boilers that share the heating and water heating in one heat exchanger will go from water to heating if only for a moment but without firing to dissapate the latent heat build up from the water firing. The banging you describe sounds more like a plumbing related problem like water hammer, is it possible that whoever did the power flush turned off the cold water stop tap for some reason and it was turned back on with a higher flow rate. Try just turning the stop tap down a bit ata atime to see if it makes any difference.
