How do I fix my Vaillant Boiler?

hi my gas boiler is a BAXI THERE IS A WATER CLOCK AND JUST BEFORE IT theres A SMALL RED TOP VALVE going into the clock is that the one u turn to let the water in its reading nearly 0 on the clock at the moment thanks a mill , will check in again , mo

maurice power
May 2009

your water pressure should be between one and two bar.

there should be a filling loop under the boiler, (silver braided hose with a little black lever similar to a washing machine valve), which you open to allow water into your system.

you will see the needle rise and hear the water flowing.. stop it when it gets to two.

the needle should bounce slightly, which is good as it shows your expansion vessel is operating.. (if that is not working it could be the cause of the dropping pressure.. but we will get to that after you try filling up and letting us know what happens....)

If the pressure drops back down at all quickly then water is escaping somewhere.. and you have a problem... either a leak in the house or your pressure relief valve (p.r.v.) is letting water out prematurely..


if the water flows for more than thirty seconds and the needle doesn't move look for a leak in the house or water coming from a little pipe outside your house where the boiler is.. that's the p.r.v. outlet if it's letting water out at low pressure it has failed and neds replacing..


don't forget to bleed your radiators too.. this wll cause pressure to drop again but gets rid of air from the system, which is very important..

your boiler will want to reset itself after having switched off due to lack of pressure.. read your manual if it doesn't do this automatically.. there may be a procedure for you to follow to kick start it..

let us know how you get on !!!

steve the biker
May 2008