Vaillant THERMOcompact VC 112/142 power recycle to ignite

[MGM]

Hi my boiler is approx 10 years old and sits in the garage and feeds a megaflow. I had issues with presure fluctuating which was down to the preasure releif valve and expansion vessel which I have now replaced. I now have had a further problem over the summer were it does not ignite following the thermostat or timer reliably and often sounds like its runnng but the burner has not ignited and will not ignite without a power cycle. I can hear the fan running and presumably the pump is ok because it often works for a few days - its now becoming more unreliable. I have also just had a massive gas bill yet I live alon and hardly use the heating - can it be using gas whilst not burning??? Perhaps its time to replace the whole unit?

Regards Mike

 

[simond]

Some thermocompacts have a water differential sensor coming off the pump. These are often replaced but it doesn't solve the problem because there is a small tube running to it which can get partially blocked. Can't visualize your model but this was a known problem.

As a result the boiler can sometimes be kept going by a number of resets but then it conks out next time it starts.

 

[MGM]

Thanks Simon, yes it does have a diff sensor across the pump. Turned off power and unplugged long tube from pump which is about 16 inches and full of bends but water flowed out freely and under preasure at the diaphram end so does not apear to be blocked; the other tube leading to the pump is only 5 inches so suspect ok too. I turned the boiler on with the diaphram disconected from the boiler chassis checked its movement, the pilot just clicks with it removed so suspect ok and reasembled. The boiler needs a power recycle if I turn down the thermostat on the front? I also can hear air running through the pipes as the boiler runs so perhaps there is a preasure problem, possibly the return flow? The hot water taps also howl until I turn them up high so again suspect an air lock from changing expansion vessel? Do you have any thoughts?

Cheers Mike