Vaillant Combi wont fire up after refilling CH system

[Delarge]

I removed and replaced a radiator on our CH system, refilled the system and was careful to bleed all radiators in the house before switching boiler back on, the pilot light is on but it does not switch main burners on - I suspect an airlock in the boiler, we seem to have this problem everytime the system is drained and refilled.

I have two questions
1) is there an easy way to solve this without waiting for an engineer
2) Any ideas on how to avoid this problem if I drain the system down again in the future?

Cheers
Delarge

 

[kevplumb]

I have two questions
1) is there an easy way to solve this without waiting for an engineer
2) Any ideas on how to avoid this problem if I drain the system down again in the future?

so do i

make and model

 

[Delarge]

it's a Vaillant Combicompact
VCW GB 221 H

 

[gas4you]

Is the auto air vent loose and working?

 

[Delarge]

we get our boiler serviced by British Gas ( you would think they'd know what they were doing) anyway I found the manual for this boiler online and found out about the auto vent thing (top right on my boiler) it was screwed down/all the way in - the manual and a sticker said this needed to be 1-2 turns out, it is now but it has not made a difference... (I guess it could be stuck how would I know if it was free?)

 

[gas4you]

Did you release it before you filled the system?

If you did and it was working you would hear an occasional 'hiss' from it as the boiler filled up.

If it was shut when you filled up, then drain the boiler and re-fill. It might help.

 

[Delarge]

I released it afterwards once I realised there was a problem... Ok thanks for the advice, will drain and refill again as you suggest and let you know

cheers
Delarge

 

[kevplumb]

there is an air release on the main h/ex

you shouldnt but no doubt you will

 

[Delarge]

no joy so far i'm afraid, emptied and refilled complete with bleeding rads etc

Didn't hear any noise coming from the auto air vent though when I refilled the system...

 

[Delarge]

I recognise that using the air release on the heat exchanger is probably not sensible as it is under the main cover but as you predicted I have and it sputtered and spat and then ran properly but has made no difference...I even bled the pump...

 

[kevplumb]

are you topping the press up

 

[Delarge]

I'm giving in and calling an engineer in... Bah humbug!

I guess I just want to know one thing....

Why? Why can't I drain down my system and refill it without the boiler airlocking each time? I had to call out an engineer a month or so ago because of the exact same problem, he reccommended that I refill the system slowly and not letting it fall all the way down but bleed a little, refill, bleed some more air, refill etc I've emptied and refilled other systems both combi and normal without ever having this problem, have I been lucky before or is there something wrong with the boiler? If the auto vent thingy is broken would that explain it?

Thanks for all the help so far
Delarge

 

[AlanE]

The automatic vent has probably clogged up and needs replacing after which you probably won't have any problems.

Having said that I repair boilers/heating systems for a living and I can assure you some systems are - lets just say challenging!!

 

[Delarge]

Ok problem solved, I cancelled the engineer and investigated the auto air release valve at the top of the boiler, tapped it a few times with the top of my finger, tapped it a bit harder (didn't reach for my hammer honest) and after a few quite vigorous prods it released a bit of air, a few more minutes of tapping away and a few more blasts of air and the boiler lit up, thanks one and all for your suggestions and help, British Gas (I have one of those homecare agreements with them) are coming out on wednesday to hopefully fit a new auto thingy...

Excellent site and thanks once again for all your help


cheers
Delarge