Our boiler continually fires up and goes out every 5-10mins giving a fluctuation in hot water temp from stone cold to hot. We have had the heat exchanger, diverter valve and main circuit board replaced with no resolution to the problem. Any ideas? some one said look at the gas valve?

Kind regards

Leonard Appleby

Leonard Appleby, October 2009

I had similar problem with a combi boiler and went through all the 'no brainer' replacements at great cost. I live in a hard water area and the problem turned out to be a furred up pipe leading FROM the gas to water heat exchanger. The bore of the pipe had been reduced from 15mm to just 4mm in three years. This interfered with the flow rate of the boiler causing it to modulate, overheat and cut out on a regular cycle. I Removed the pipe and cleaned out the scale with a rat tail file. Worked a treat.

Mike Smith, February 2010