Vaillant Boiler Problem

[tremor]

Hi,

I've got a Vaillant THERMOcompact VU 242 Boiler. The ignition light keeps flashing which according to the service manual is a poor water circulation problem. The problem seems to occur when the boiler has been on for a while it may be operational for several hours and then the ignition light will start flashing. If you reset the boiler it works fine and will continue to work for a number of hours before the same thing happens again. Vaillant said to check the pump which seems to be working fine. Is it possibly the differential pressure switch? I drained some water out the system to check for corrosion and sludge; the water smells a bit of chemicals but is otherwise clean with no apparent corrosion present. The water pressure on the central heating side is 1.2 bar. Before I spend money calling someone out, does anyone have any ideas what could be causing the problem. Other than suggesting the pump Vaillant haven't really been that helpful and I'm out of ideas? If it is the differential pressure switch on it's way out can I change it myself?

Thanks in advance for any help and advice.

 

[kevplumb]

possibly cr*p in the pipes to the switch (only a thought)

 

[tremor]

If it was rubbish in the pipes to the switch wouldn't it fail to ignite when the boiler is reset? The pressure when the system is hot is about 1.7-1.8 bar and it does it more frequently when the water is hot. If the water is cold it will normally happen after the water has reached about 70C ie when the pressure has increased.

 

[ChrisR]

Take all the operating bits apart for a clean and grease. Sorry can't remember which bit exactly it is.

Can be the pump running slow of course. Run it with the head off, you should NOT be able to stop it with only medium finger pressure.