pressure loss problem on combi, no water from expansion vessel valve

[andy16v]

hello all

ive got a problem with my ideal c80ff (not ideal i know!!)

ive had water leaking from my prv which meant topping the boiler up nearly everyday. after browsing the forums i checked my expansion vessel for damage to diaphram/ air pressure.

after depressing the valve there was no water present (which im presuming means it isnt knackered) but on the same token there was no air pressure either.

the prv is clogged up which is causing water loss even when the boiler is off but im awaiting a replacement.

thing is, is i dont want to replace the prv till i know ive sorted the pressure vessel problem.

what could cause it not to hold pressure if the diaphram is in good working order?

im going to drain the system when i change the prv which im presuming would be the best time to recharge the vessel.

but how will i tell if the schrader valve is faulty? i dont want to charge the vessel and change the prv only for the thing to go again.

any help is greatly appreciated

andy

 

[mikegas]

pressurise the vessel and then spray ldf on the valve

 

[WHPES]

You can tell if the schrader valve is faulty in the same way you can with a car - squirt some diluted washing up liquid on it and watch for bubbles. If faulty nip down to Kwik Fit / ATS etc for a new one.

 

[andy16v]

first off, thanks for the replies folks.

the vlave is on a brass fitting which is screwed into the vessel body. maybe i could hit it from all angles and remove it completly and wrap some ptfe around it? just didnt want to screw it out if its gonna affect anything.

and forgive my lack of plumbing knowledge but what is ldf? and what effect will it have?

thanks again

 

[GrahamM]

The valve is a schrader valve found in most car tyres. You can remove it by using a valve key and replace with new valve if you suspect it passing. Open a drain valve on the central heating system. Use a foot pump to pressurise the vessel to 1 bar approx. Close the drain valve. Refill the system to 1-1.5 bar. Switch on boiler. Job done.

 

[Blackcatgas]

Youve pressed the valve in and no water comes out of the vessel, and theres no air escaping, try a foot pump (youl have to use your hands unless your 1970s/80s commodores front man Lionel Ritchie in which case you be able to dance on the cieling and operate a foot pump), pump the vessel up to what It should be? 0.8 bar ish, see if that works, take the pressure in a week, is it still at 0.8 bar?.

Edit sorry didnt read Graham Ms post, beat me to it.

 

[Micky T]

I have a combi with a slow pressure drop ie 1.5 to zero in about two weeks. There are no leaks showing anywhere and no evidence of any water through the safety valve.
Someone suggested there must be a crossover leak in the hot water heat exchanger.I can picture this happening when a hot tap is open and therefore the heating pressure is greater then the mains, but the problem I have with this theory is why doesn't the mains pressure when static push up the sealed system pressure especially at night when it definitely goes above 3 bar, any explanations?

 

[Killy Bing]

Well, that persons an idiot.

get a gas safe engineer in, tis a common issue.