Vaillant VCW GB 240H...Central Heating Problem...

[goddamnvaillant]

Somebody please help me!!! The sodding bolier is playing up again. The hot water out of the taps seems to be heating up nicely, but the boiler only kicks in the central heating when it feels like it. I have recently removed 2 rads due to recorating and have linked the rads out with a joining pipe between flow and return on each rad. When the ch comes on, it warms the rads up, but then goes off for ages, and then comes on randomly. The room temp is about 10c and the thermostat is set to 25c. Ive even linked out the terminals that connect to the timer so the "run ch signal" is on all the time. The system was emptied and bled. The heat exchanger and pump have been opened up and no air comes out.

Somebody help please as it's sodding freezing...ice forming on end of my nose

Thanks All!

 

[petit_pablo]

You need to check if the diverter valve is moving the microswitches across when in CH mode and keeping them closed.

 

[goddamnvaillant]

Thanks Mate. i checked the divertor valve and the shaft does move the plate , and it does operate the microswitches...well one of them anyway!? The top microswitch operates on and off, but the bottom microswitch doesn't get actuated by the plate. I have checked the switches with a DMM and they are fine. Looking at the wiring diagram, the top one is NO and the other is NC. Regardless of what the divertor valve does, the NC switch can't change state. Is this normal, as it seems abit odd?

I powered the boiler off and when i turned it back on, after flicking the lhs switch to ch and dhw (from previous dhw) nothing happened for a while, then it moved the div-valve, the burner fired up, big flame, reduced to small flame and then went off.........

Thanks......

 

[petit_pablo]

Sounds like it could be the modulation control on the Gas valve then. Did it go to low flame then just drop out? Does it do this every time?

The microswitch action you discribe is normal, as is the delay before firing CH

 

[goddamnvaillant]

Sounds like it could be the modulation control on the Gas valve then. Did it go to low flame then just drop out? Does it do this every time?

The microswitch action you discribe is normal, as is the delay before firing CH

It goes pilot, high flame, a few seconds later, low flame, a few seconds later out and back to pilot. Although, the few seconds (about 10 sec) can be longer (about a minute)..... and it is the same every time....

 

[DP]

Suffice to say this boiler is a complicated oiece of machinery. To give an answer on the forum without onsite diagnosis is like looking for a needle in a haystack.

Would initially suspect the water section area of the boiler. Follow previous advice at your peril as boiler function correctly for HW, therefore nothing wrong with modulation.

Unless you or the guy that looks at the boiler, understands its operation, only then he/ she stands a chance of repairing it.

Resist temptation to replace the boiler. You will not find a boiler well built as the one you have.

Only thing wrong with this boiler is that it DOES not fail very often. So one forgets a lot when one comes across onother on its knees

 

[goddamnvaillant]

Thanks everyone! I really appreciate the help, and as you say, I think I'll have to get a pro in.

When I get it sorted, I'll post up what the problem was...

Thanks.