Boiler dropping pressure when heating turned off

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Hi just after some advice or if there is anything I can do before calling an engineer out.

We have been in our home 2 years and the boiler is about 10 years old baxi duo tec 33 boiler I believe and never had an issue. We are having a problem now where as when the heating is on its perfectly fine and will stay on without fault until I turn it off but after being turned off about 30 mins or so after being turned off the pressure completely drops and needs topping back up. If the heating isn't on the boiler holds pressure as it will do when the heating is on but like I said completely drops after being turned off. Is there anything that I could try myself?

Many thanks
 
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Expansion vessel problem , possibly.
When heating is on ,does pressure increase to around 3 bar ?
 

CBW

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Check the safety discharge pipe, usually ran outside in copper. If it’s dripping the. Likely an expansion vessel issue or prv issue.
 
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Thanks for both replies

As its under the stairs I have never looked if the pressure goes up i just top it up and turn heating on and come away.

I have checked that pipe and nothing comes out of it.

I have spoke to a work colleague who is a plumber and he has mentioned either a leak or expansion vessel problem. but I've never been able to get him round to diagnose!
 
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Yeah I will do and ill let you know will be tomorrow tho now. If I remember correctly I've watched once and it didn't go up but not 100 percent sure of top of my head. Need to get it sorted tho Mrs is pecking my head lol
 
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Ha ha ,join the club mate !
Leave c/ heating on for an hour then check pressure.
 
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Well if the pressure doesn't rise significantly when central heating is running then the expansion vessel would appear to be working.
Does the pressure drop to zero 30 mins after turning heating off ?
And does it happen every day the heating is used ?
 
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Quote " I have checked that pipe and nothing comes out of it."

Check it by tying a bag over it.
 
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Well if the pressure doesn't rise significantly when central heating is running then the expansion vessel would appear to be working.
Does the pressure drop to zero 30 mins after turning heating off ?
And does it happen every day the heating is used ?

Yes about 30 mins after turning the heating off and it drops every time.

Gonna go tie a bag to it now and check in morning
 
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A system with a flat vessel and no air in radiators will lose a tablespoon of water and fault.
A system with a full vessel and a bit of air in the radiators would take a long time.
 
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Just gone out to the bag this morning and it was damp with a tiny little bit of water in the bottom
 

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