Vailant VCW GB 240 - Central Heating failure

[Frimly Greendish]

Dear All

The wonderful people on this site identified an obsure problem with my boiler nearly a year ago and saved me loads of money! Now I need your help again, please

Just advanced the central heating to turn on and nothing. The boiler is working perfectly for DHW, but it does not fire at all when CH switched on. No water circulating (so far as I know), nothing. THis has happened suddenly - the CH was fine yesterday.

Any ideas would be gratefully received - its cold here!!

Thanks very much.

Al

 

[Frimly Greendish]

A bit more info. I have heard the boiler briefly attempt to fire twice in about 30 mins. There is a click immediately followed by a whoosh of igniting gas and then nothing - only the pilot light is burning.

Any ideas please lads???

Al

 

[MANDATE]

When I hear HW is OK and CH does not work, I think '3 port motorised valve' stiff spindle? motor failure? or micro switch failure?
Do you have such a valve? I bet you do!

 

[scatmanjohn]

Do you have such a valve? I bet you do!

I bet he doesn't

 

[Frimly Greendish]

I dont know if I have this valve in the boiler. It is a very old boiler and apparently it is horrendously complex.

Anyway, more information which might help. I have just turned the boiler off completely and left it for a few minutes. Then I turned it back on (with the CH in the on position). There was a click/switch noise and the boiler immediately fired up. It burned for about 4-5 seconds and then it went off. SO it fires up, but then something happens to make it close off.

Any more ideas?

 

[Frimly Greendish]

Sorry to bore you but yet more info which may narrow down the problem. Ive just gone throught the same procedure, turning it off and then switching back on again a few minutes later. The following happens: -

1. The boiler fires and burns for about 5-7 seconds and goes out.

2. As soon as I switch it on there is another noise which I am almost certain is the circulation pump. This keeps going after the boiler has stopped burning.

So I assume it is nothing to do with the pump.

Please help - we are freezing

 

[Frimly Greendish]

Please help I & I

 

[The831Bunny]

I'm afraid there is no easy answer to diagnose your problem without checking the hydraulic diverter valve operation. In order of 'probability' though...

1. sticking servo valve
2. blocked hydraulic tubes
3. stiff diverter valve spindle/gland
4. leaking water section/corroded coupling piston
5. Diverter valve diaphragm

Hydraulic problems are very difficult to diagnose and involve an in-depth knowledge of the boiler's operation. My advice would be to contact a RGI who is competent repairing Vaillant appliances. Vaillant themselves offer a fixed price repair service.

Bunny

 

[Frimly Greendish]

Thanks very much Bunny - very helpful. Co-incidentally (or possibly not) the boiler has just developed a small water leak, which appears to be coming from a connection to a very complicated piece of machinery on the lower rhs (as you look at it) of the boiler. Could this be connected? As for the diverter valve, I had the diaphragm replaced about 9 months ago to cure a problem of no hot water, so maybe not that?

Cheers

 

[gas4you]

Is this another one of your wind ups grimly?

 

[The831Bunny]

Thanks for the reminder Dave...

I'll take a back seat

 

[Frimly Greendish]

Oh for heavens sake! I knew I should have changed my name!! No, I swear it is not a wind-up at all. Last year you guys really did solve my boiler problem (diverter valve diaphragm I think from memory) but I admit I did engage in some infantile antics along with a mate of mine. It all started because no-one responded to my initial cry for help, so I created a new ID, pretending to be a RGI and I responded under that ID and gave a nonsensical piece of advice. That final tempted all of the brains on the site to contribute, and it sort of grew from there. Me and a mate created multiple IDs, and had a bit of a laugh. I am really sorry if I offended anyone, but I swear my boiler problem is genuine! I have a crappy ancient Vailant and I cant afford to shell out £2K plus for a new one, so need to keep it alive for the rest of this year if poss. Please help me!

 

[Gasguru]

Just for starters..

Remove the right hand side white casing panel.

Pull off the clear plastic cover over the diverter microswitches.

Note the switch position at rest with the boiler off.

The diverter will shunt left and right depending on whether there is a hot water or heating demand.

Check in heating mode the diverter continues to keep the microswitches activated.

If so next look at the gas valve differential operator (the bit on the front with two small control pressure tubes). I think from memory you can see the operating pin moving by using a dentists mirror.