Unvented System losing Pressure

[TahirJogiyat]

Hi Guys
Appreciate some help with my boiler and unvented cylinder system which has been losing pressure fairly rapidly over the last week or so.
To date we have checked the PRV valve, expansion vessel within the boiler and heat exchanger. Yep n addition a visual check of all the pipe work yet still no solution.
Could there be an issue with my unvented system which is causing my boiler to lose pressure? What other checks need to be carried out.
I have lifted a couple of floorboards on the ground floor to see / hear any leaks but still nothing.
Lastly when the engineer initially came he used a couple of bottles of the leak sealant which seemed to solve the issue for a couple of days but as soon as the hot water went on the system started losing pressure and now it loses pressure both with heating and hot water. Makes me wonder if there is an issue with my unvented system.

Any advice would be much appreciated.

 

[terryplumb]

You are losing water out of the sealed system somewhere.
Does pressure rise to around 3 bar when heating is on ?
If no water is dripping from the PRV pipe outside, that really only leaves a leak on pipework,or within boiler, or leaking heat exchanger.
Do you have any pipework buried below ground floor level,in concrete or a void ?

 

[TahirJogiyat]

Thanks for your reply Terry - we have pipes between the void which hopefully someone will be able to access the entire ground floor. Do not believe there are any pipes buried below concrete. Can I rule out any issue with my unvented system?

 

[terryplumb]

I very much doubt your unvented hot water cylinder has anything at all to do with your central heatings sealed system losing water/ pressure.
If you top pressure up to just over 1 bar ,how long does it take for pressure to drop to near zero ?

 

[TahirJogiyat]

Probably a couple of hours - as mentioned I lifted a couple of floorboards to check / listen for any leaks but nothing picked up this far. Think I read somewhere to drain the system completely and locate the leak via an air check - is that correct?

 

[terryplumb]

Don't know what you mean by an " air check". It doesn't take a great deal of water to be lost for system pressure to drop to zero , a lot less than a quarter of a cup full would do it.
If you close the boilers flow and return isolator valves ( top pressure upto 1 bar first),and leave the boiler not operating for a few hours ,if pressure drops that's an indication that the water loss is via the boiler.
If it doesn't drop ,open both valves ,if the pressure then drops immediately the water is lost on the system , pipework/ radiators.