Vaillant ecotec plus 624 overheating

22 Jan 2012
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United Kingdom
Hi, I'm a newby to this valuable rescource and I cant seem to find anything relating to my problem

After 3 years fault free, our Vaillant ecotec plus 624 [ all new installation ] has started to play up.

After several failed cold starts [and call outs], the pressure sensor was replaced 2 weeks ago and all was well again

But now the water flow temperature slowly gets too high and the boiler shuts down [ runs on ] for about 5 minutes when the flow temperature exceeds the set temperature by about 5 degrees. The boiler then re ignites runs for a while and the cycle repeats itself.

There are no fault codes showing.

This happens on both HW and CH as we have a seperate HW tank [ with emersion heater ]

It would appear to me [ a retired maintenance engineer ] that the gas modulation is cutting back but not quite far enough.

The 10 radiators all get nice and hot fairly quickly so the circulation seems to be good, the system has been serviced twice since installation and this fault occurs whether the set temperature is set higher or lower.

Any advice would be most welcome as I hate to think what the heating engineer will charge for lots of watching the boiler very slowly overheat.

Many thanks
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