Ecotec plus losing water?

[Knappers]

Hi guys, any ideas on my pressure problem?
Friends boiler keeps loosing pressure, went out today to check the usual suspects (expansion,prv,system leaks, heat exchanger) but didn't find any issues.
stopped for a chat for about an hour and checked system pressure when boiler was up to temp - all good.
He's just called (only 3h later) to say its dropped out again?
Am I missing something?
Is the heat exchanger prone to leaking at particular temp?
Takes a good 700cl to drop to 0, where's it going???

 

[ShaunCorbs]

Tie a bag to the prv

 

[Scott_D]

Has it got a digital or manual gauge?
Could be the pressure sensor

 

[Knappers]

Tie a bag to the prv

Took pipe off and dry as a bone, doesn't look like its ever operated and pressure doesn't get near 3bar.

Has it got a digital or manual gauge?
Could be the pressure sensor

Both and both fine

 

[Scott_D]

maybe top up the pressure and then isolate the boiler from the system for a few hours to confirm which is loosing pressure

 

[Knappers]

maybe top up the pressure and then isolate the boiler from the system for a few hours to confirm which is loosing pressure

Good call, will keep my fingers crossed that the valves don't leak.
Thanks

 

[Knappers]

I've been back and still none the wiser.
Whent over all the pipework, watched the condense for drips when cold, put a latex finger over the prv pipe (after i fished out a spider and bit of bone-dry mortar)
Isolated heating circuit and checked for pressure loss after an hour or so.
Vaillant are going out on Tuesday so I've left the heating isolated and told my mate to turn it back on after 24h and that if it drops straight away its definitely a leak on pipework and to cancel Vaillant, then we can try some leak sealer i guess?

 

[MgRev1]

Knappers, habva you found a leak?