Vaillant VCW GB 221H Won't fire up

So you've checked all the opther stuff like NTC and 20voltsDC on the gas valve? That microswitch (mentioned page 64, "see 14.23")??
Yellow LED on?
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It's looking like one of those where there's a bad connection or something they didn't think of when they did the manual.

That 20vdc on the gas operator has to be the critical question - if its there then there should be gas, if it isn't then the prob's a sparky one.
yes fellas all those have been checked and me and my bro in law are also stumped.
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Its been tested with a multimeter and appears to be there, how else wopuld you test for it.

In the manual the fault finder says if it is available then replace to gas operator. If it is there what problem would it cause where you have to replave the operator. if is isn't what is that problem?
The voltage would open a valve with a solenoid, You could check the connections on the gas operator for continuity - probably of the order of several hundred ohms, rather than 10 or a megohm. If it looks reasonable then depending on the construction you can often feel the magnetic force by dangling a screwdriver in the right place. I don't know whether its possible to change the solenoid without the whole valve.

If the volts aren't actually on the pins on the gas valve then I guess it looks like the connections between the pcb and the gv.

Unless the gas is off :rolleyes:
will have a try at checking for 20vdc againa dnsee what we can come up with. will let you know.
Remove combustion chamber cover and locate left hand tube to heat exchanger. At the top of the tube locate a bleed screw. Undo half turn to let any air bleed out. Close when water dribles out.

Locate auto air vent rear top right of boiler. insert a paper clip wire into orfice to be greated with a spurt of water. If none comes out, change auto air vent.

Run boiler in CH mode while watching the diverter mounted microswitches. Plunger will be expelled from the diverter valve to operate the microswitches.

Check above and come back.

Only act on above information if you are CORGI registered.
if DP's suggestion still gives no joy I would look at the pressure differential valve aka pump proving switch

one of the two small supply pipes to this may be partialy blocked or airlocked

You could pressurize boiler to 2 bar to see if that clears it. You will need to reset pressure to 1 bar when you get it working
Thanks will get some one to carry out instructions will let you know.
finally got soemone to look at it, reckons the gas pressure governor has gone so it will need replacing.
Recon nothing. Either carry out diagnostic checks or throw the towel in and start changing parts.

If you follow the advise given, the boiler will be fixed. Change the governor and nothing happens what do you do then? Advise is already on the post. You owe it to all those that have tried to help you. Perhaphs all of us have wasted our time.
Not wasting time, advice very much appreciated

bleed screw fine
air vent replaced
miscroswitches working
pressure increased.......still no joy

all advicse carried out prior to identifiing the gas governor as problem.
gas pressure governor replaced and boiler now fires up. So far so good, HW and CH working. thanks to all who helped out with advise.

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