Combi losing pressure

dal5band · 23 Dec 2014

Boiler model Vaillant Turbomax - 837 E approx. 10 years old.

My mum's boiler was running fine until I noticed one of the radiators had air in it and I bled it. I had to top up the water to bring the pressure up to normal. Now, it keeps losing pressure over a few days. I can't see any obvious leaks anywhere - but there is a drip on the pressure relief pipe outside. Seems by topping it up I triggered something.

Just want people's opinion - would it be the relief valve or the pressure vessel ? It's under maintenance - I want to be prepared to argue the toss when I call the engineer next week.

Thanks in advance

Dan Robinson · 23 Dec 2014

Could be either or both.

Easy to check.

The bleeding of the rad was more likely a consequence of the failure rather than the cause.

Just don't say anything to the company about bleeding.

StevieV1 · 23 Dec 2014

Several possible causes. I had this issue several years ago and tracked it down to the diverter valve - It was letting some of the CH water through the DHW side so pressure was dropping - resolved by changing the diverter valve.

Bunnyman · 23 Dec 2014

That's the biggest load of ****** I've ever heard? If the diverter was passing it won't affect pressure in any way, an if it did the pressure would rise not drop as mains pressure is always higher than heating pressure lol

StevieV1 · 24 Dec 2014

So if water was leaking from the sealed CH side into DHW side and was not replaced via the filling loop, the pressure wouldn't go down? Got news for you, it did on mine. OP was asking for possible reasons for his pressure drop, I provided one that happened to me. But you obviously know better so....

Try reading my post properly

dal5band · 24 Dec 2014

UPDATE : It seems it's holding steady at just 1/4 bar - just in the green zone and the boiler is still working so I am leaving it alone. It's the topping up that caused the relief valve to drip - will get it fixed at a more convenient time.

Original Poster

Bunnyman · 24 Dec 2014

Sorry stevie u obviously dont understand systems or grasp the physics of it

If mains pressure is 1 bar plus ( which is the legal minimum) if there is any crossover from heating to mains it cannont physicaaly go below 1 bar can it, someone bin pulling ur leg

ALCPlumbing · 26 Dec 2014

I thought the minimum was half a bar. Irrelevant and unimportant but just wanted to check.

sooey · 26 Dec 2014

Just want people's opinion - would it be the relief valve or the pressure vessel ?

Sounds like the pressure vessel wants topping up, the rad with air in it was acting as a vessel till you bled it.

dal5band · 27 Dec 2014

Ahh !! Sooey, what does topping up the pressure vessel involve ?

denso13 · 27 Dec 2014

//www.diynot.com/wiki/Plumbing:faq7

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Combi losing pressure

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