I must have a leak but I can't find it...

[diligentdave]

My Biasi combi boiler keeps losing pressure. Sometimes it can take all day, other times it can be within 30 mins!!
I have been round the house and checked every visible pipe, radiator, bled the system a few times after refilling to dispel air, but no matter what, I keep losing my pressure.
The pipes outside (from what I've read this is the PRV pipe) are clear, there's nothing coming out, no air or water, so the question is,each time I refill the system with water from the filling loop and recharge the pressure, where the hells it going to? Am I losing water or just pressure or both? I feel really thick here....

 

[SpecialK]

Top up system to correct pressure with boiler off, then isolate the boiler from the heating system using the valves underneath.
Does the pressure still drop?

 

[MANDATE]

most likely going out through the PRV and evaporating.
Why not start with observing the pressure while cold then put heating on and watch the pressure gauge rise and if it reaches 3bar it's going to activate the PRV.(indicating expansion vessel problem)

Also the PRV may have already been activated at some stage and not properly sealed when it closed again. This is due to sediment between washer and valve seat. (secure plastic bag on discharge pipe ans see what it collects)
Of course you could have both the above problems.
Otherwise the AAV automatic air valve could be the source of leak
You can still follow specialks suggestion which will indicate which side of the valves is the leak.

 

[45yearsagasman]

You will almost surely have a leak after turning those valves on and off.

 

[diligentdave]

Thanks for the replies. Just out of interest, I topped the system up last night to approx 1.4 bar (operating pressure) at 11.30, I checked it this morning at 5.30 and it's now at 0.7 bar, without running anything overnight.

Does this indicate anything, other than I'm losing pressure somehow?

 

[MANDATE]

PRV not sealed fully?
Expansion vessel losing air allowing diaphragm to move across so it holds more water and less air?
Auto Air Valve?
As you say the water s got to be going somewhere

 

[jono_h]

Leaking pipe under the floor?

(I had this last week - nothing to see because it was under the ground floor floorboards, but it looked lik a swimming pool down there!)

 

[adlplumbing]

try injecting the system with leak sealent