gascob

you can take the plate heat exchanger out and give it a good rinse out through a tap whilst giving it a bit of a crack with some grips or a screwdriver, you should see some chunks of debris coming out.. if you live in a hard water area it could be scaled up which you will struggle to get out(i do know people who have soaked a plate in calgon overnight though) they are easy to take out on a performa but make sure the 4 washers are intact before you put it back together or it will be leak city.... i suspect the low gas will be ok with the ch being fine...