Systme Pressure drops to almost Zero even after Repressuring via bypass loop

nnj10

I am having some real problem with my 6 year old combi boiler, just been noticing for tha past week or so. My combi boiler's Pressure Guage drops to 0, I then open the bypass valve to repressurise to between 1-1.5 bar, but it would then drop again to zero in matter of minutes.
I even tried once to set my pressure to 2.5-3 bar and no joy.

This would suggest that there is some leak in the system.
But where? How do I find a leak.
Obviously not using CH at the moment, but DHW still works as usual.
Could there be a problem with Pressgure Guage?
Also noticed that boiler makes some humming noise when used for hot water after pressure drops to zero.

keystone

Go outside now and see if you have quite a bit of water coming out of the PRV pipe. Thats the 15mm copper one. If you do then at some stage the PRV has lifted 'cos the pressure got too high. Trouble is that when that hapens they get full of carp from the system and don't reseat properly so you get a permanent leak.

Cheers

nnj10

Thanks for a very quick reply.
No, there is/wasn't a relief valve discharge due to overpressuration.
I think now my problem is systen does not hold pressure at all, so something's definatley wrong, and I see no evident leak anywhere in my visible pipework/radiators etc.

keystone

nnj10 wrote: »

Thanks for a very quick reply.

S'OK - just happened to be scanning this particular part of the forum when you posted.

No, there is/wasn't a relief valve discharge due to overpressuration.
I think now my problem is systen does not hold pressure at all, so something's definatley wrong, and I see no evident leak anywhere in my visible pipework/radiators etc.

Have you checked your expansion vessel? It might just need recharging. Open the "car tyre" valve. If air comes out - repressurise it and then see what happens. If water comes out the diaphragm is knackered and you need a new EV.

Cheers

gas4you

Yo lose pressure that quick there must be a serious leak or the prv is letting by.

Re-pressurise the boiler and go out side again to check the relief pipe is not running or dripping.

If it isn't, pressurise boiler to 2 Bar, shut isolating valves under it, leave without using it for as long as possible.

If pressure drops, then the leak is in the boiler. If it only drops when valves are opened then leak is on system. Beware though, that some makes isolating valves may leak if they are moved.

Only you can decide whether to try this.