0 bar pressure in combi boiler

[Tudor]

Hi folks,

I have a Vaillant Combi Boiler, either a VCW-GB 242 EH or a VCW-GB 282 EH, can't seem to be able to confirm this. The hot water from the taps is working fine, problem is with the central heating.

The central heating did not come on this morning and the pressure gauge was registered at about 2 bar, which is what I thought the problem was. I dug the manual out and found the pressure release knob, and release some of the pressure so it was just above 1 bar. For some reason, it has now gone down to 0 bar, and when looking at the manual it recommends getting the system topped up.

1. Do you think the central heating did not come on because the pressure was too high?
2. How do I go about topping up the system to approx 1 bar, the manual says to get a plumber in to do it?
3. Is there a few other things I can check that may have caused the central heating to have failed?

Thanks very much.

Dan.

 

[ChrisR]

1. No - so now you've caused more trouble!
See the Faq section on pressures.

3 Not without fairly detailed understanding, could be so many things.

 

[Rob]

Its unlikely the 2 bar pressure was causing your heating not to come on.

By opening the pressure releif valve to drain some water means it is probably now constantly letting water out as they never re-seal properly. It will probably need replacing.

To top the system up you need to locate your filling loop. usually just under the boiler. Its a metal braided hose linking two pipes together. Open the tap/s till the guage rises to one and turn off.

You will keep losing water though untill the pressure releif valve is changed or repaired.

 

[Agile]

You should never open a pressure relief valve to drain water as they will be unlikely to reseal.

Your boiler will have failed to start for another reason.

I assume its not working on DHW or CH ?

Tony

 

[Tudor]

Ow cr*p

Thanks people.

Tony - Boiler fires up no problem for hot water.

Rob - I have noticed a pipe that runs from the boiler to the outside wall, which appears to have been dripping a bit. I take it this is where I am loosing the water that you refer to?

Thanks.

Dan.

 

[Agile]

Your model is very unlikely not to work on CH.

Have you checked the room stat and timeclock?

Tony

 

[Tudor]

Thanks.

I have located the filling loop and have managed to get the pressure back to 1 bar, and fired up the central heating. The pressure valve must be leaking as I can see some water dripping from the pipe running to the outside of the house.

I will speak to our plumber tomorrow and explain that I have been a bit of a tw*t and that I most probably need a new pressure valve fitted, and at the same time he can do a service and check everything.

The wife keeps telling me to leave things alone, nevermind

Thanks very much to all of you for your quick help, most appreciated.

Dan.

 

[Tudor]

One last question folks.

I managed to fire up the central heating when the pressure was back up to appox 1 bar, the radiators seem reasonably hot. The pressure has dropped back to zero, due to the PRV leaking, should I switch the central heating off altogether????

 

[ChrisR]

Try twisting the head of the PRV until it clunks back onto its seat. SOmetimes you can get them to seal a bit better.
If it continues to leak, put the pressure up to about 2 and you can run the CH as long as it has pressure in it.

 

[chrishutt]

It's often possible to clear the debris off the washer and seating of a PRV with repeated opening and violent closing (the older Vaillant ones had a lever rather than a rotating cap), or even dismantling and cleaning it.