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alex hewitt
alex hewitt, Plumber and electrician
Category: Plumbing
Satisfied Customers: 108
Experience:  Corgi registered plumber, Nic/Eic registered electrician.
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my boiler is losing pressure does this mean i have a leak or

Customer Question

my boiler is losing pressure does this mean i have a leak or could there be another explanation we have recently put 2 extra double radiators on and the heaters were running fine until we recently blead system since then the pressure keeps dropping
Submitted: 8 years ago.
Category: Plumbing
Expert:  alex hewitt replied 8 years ago.



Number of reasons why it could be losing pressure.


1 A leak

2 Faultly expansion vessel

3 Faulty pressure relief valve

4 Faulty auto air release valve

5 Air being released trough the auto air vent.


Given that you have just added some radiators and bled the air out there is probably alot of air left in . The auto air vent will release this air slowly overa few days and as a result the pressure will drop.


Best course of action top up the system to around 2 bar and monitor it. If drops over the next couple of days top up again. It should settle down within a week if not some fault finding is in order.

Hope this helps



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Customer: replied 8 years ago.
we have been topping up and monitoring boiler for about a month the boiler is a valiant ecotec 831 and it has been in for just over a year the other problems mentioned are they a typical fault to this boiler
Expert:  alex hewitt replied 8 years ago.



No they're not typical to any boiler this new.


I would say that 2,3 & 4 are unlikely causes in a fairly recent installation.


A quick couple of tests will rule these out.


Check the pressure relief valve vent ( 15mm copper pipe to outside) for dripping. Should be dry.


With the gauge reading about 2 bar turn the c/h on max ( turn up any room stats etc to max)


Watch the gauge as the pump and burner kick in. The pressure should rise maybe a 1/4 of a bar then stay the same. If the pressure continues to rise as the boiler gets to heat it will finally get to 3/3.5 bar and the pressure relief valve will open and reduce the pressure.(this would indicate a vessel with no charge )


Find the auto air vent in the boiler it looks like this



Check the top around the cap isnt crusted and wet , the cap should be loose by a couple of turns.If yery wet and crusty this would indicate the float inside isnt operating and either clean or replace.


If none of the above I,m afraid you are looking for leaks.


Hope this helps