vailiant turbo max hot cold fluctuating water temp?

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