DHW works fine, Boiler on with tap opened, off with tap closed, but reignites after a few seconds on low flame with CH switched off. As soon the power is applied to the boiler the CH pump comes on the fan runs and the boiler ignites on low flame with thermostat in the off position. Help!!

Moses, October 2005

water valve sticks in hw position which works by presure diferential,wen a tap is opened a needle is pushed upwards operating a microswitch on the servo valve which then fires the boiler,with age the water valve corodes and sticks and the needle stays in the extended position making the microswitch which keeps the boiler on even tho ther is no demand for heating or hw,you can get a service kit for the water valve but would recmend just changing the water valve and the needle/spindle making sure you clean and lubricate the spindle housing with silcone grease..to check look at the back of the servo valve black sometimes white depends on age with 4 presure differential tubes atached..with no taps on check that the switch behind it isnt made..if it is try push the needle/switch arm back into position manually..email me if you need more info ...ctokeley at hotmail co uk hope that helps dude

toke, September 2009

There was a pin actuator that was also corroded but that the engineer had not encountered before. Allegedly now fixed.

motco, January 2006

Update: The problem still exists but slightly less intractable. Vaillant visiting again in a couple of days - all in the first call-out cost, I hope.

motco, January 2006

Well, £195.00 poorer and I know now that it was the water valve, not the servo valve. Vaillant service engineers are well trained and come when they say they will.

motco, January 2006

This site is only as good as the spirit of the users. When you solve a problem, tell us about how! You should take information of course, but give a bit back or it won't work!

Happy Christmas.

motco, December 2005

Moses, do you have an installation and service manual? If not, let me have an e-mail address and I can scan the relevant pages and send them to you. Check that the return spring on the servo is intact. I am not a service engineer, just an owner and I'm trying to sort it myself. Actually it's my son's flat and I cannot get access often as he's at work.

motco, November 2005

hi motco,
I will try to service / replace the servo valve at the weekend if i get time and then let you know.
Many thanks 4 ur feedback.

Moses, November 2005

Moses. I have been in touch with Vaillant Tech people and they say it's more than likely a sticky servo valve. As I see it only the servo valve or the diverter valve CAN be responsible. There is supposed to be a return spring on the servo valve - check that. I cannot get to mine for a few days, it's in my son's flat and he's out working a lot. If you want to e-mail me my address is callom@yahoo.co.uk

motco, November 2005

No I haven't fixed it yet, I don't know whats wrong. Someone out there, surely knows what could be on the blink,and can help us!!

Moses, November 2005

Moses, I have pretty well exactly the same problem. Have you fixed yours yet?

motco, November 2005