I have a Baxi Combi boiler and when running the hot water it is curently going form hot to cool in 30 sec spells when running the bath

Peter Lorraine, October 2005

I had exactly the same problem on my Baxi Genesis 80. Eventually the problem got worse and the hot water would run for a few seconds and then go cold but at first it cycles just as you describe. It turns out that the heat exchanger was blocked with small bits of metal that had flaked off from the inside of the radiators, and changing it solved the problem! Hope this helps!

Paul Cooper, December 2005