Thank you! Boiler was installed by builders 3 years ago and all corgi passed, but have fallen out with them so don't want them back. In the last couple of months, the hot water has been fluctuating from hot to tepid and at the same time the flame rises and falls by a noticeable amount. I've reduced the flow rate but that hasn't helped. Someone has told me it might be the plate heat exchanger, which I believe can be cleaned easily, or possibly the air pressure switch. I understand that it's unsafe to start working on gas myself but would like to know what the problem could be so that if I