How do I find the pressure leak on the baxi 105e boiler?

Dear all thank you for your help, I have established that the leak is in the system and not on the boiler. a lot of the pipes are under cement, would you advize banging through and trying to find it or is there a way of repiping it but in a way that it cannot be seen. How much would this cost? its a 2 bedroom ground floor flat 5 radiators...
thx Louise

Louise Birch
July 2007

Started to write answer but got called away. Came back later and finished answer and sent. In the meanwhile Hi-spec had responded.
Better two replies with the same solution than another question from someone who didn't try to help. But, if that's what rocks your boat......

T.h.s
July 2007

that's already been mentioned in the first answer.
why say the same again.

steve moss
July 2007

To find out if it's the boiler or the system, you need to locate the isolation valves under the boiler(they should be the far left and far right one's).
Top the boiler up to normal ,around 1-1.5 bar then turn the valves off (you won't be able to use it for hot water or heating while it's on test, so you MUST turn the power off to the boiler completely)
Leave it overnight and check if the pressure has dropped or not.
If yes it's the boiler.
If no, turn the valves back on and see if the pressure changes.
If it's in the system you will have to find out where(could be radiator valves or on the pipework)
If it's the boiler it's most likely the pressure relief valve that goes to the outside or the auto-air vent or the expansion vessel.

T.h.s
July 2007

>I have replaced the pump.

why that won't cause a pressure problem.

> How do I establish where the pressure leak is

first check the copper pipe that exits the bottom of boiler and exits to an outside wall (overflow)
see if thats dripping or been dripping.

if so then you have a faulty prv.


if not then you must have a leak in the system could be anywhere underfloor, rad valves etc.

how long before pressure hits 0 from 1.5 bar ?

hi-spec plumbing
July 2007