Greenstar 30si Combi - Pressue over 3 Bar when just C/H on

[thewigster1976]

Hi All,

Current Normal Pressure = 1.5 (hasn't been topped up for months)
Just Hot Water being used - pressure remains at 1.5
Just C/H on, the pressure quickly rises to just over 3
Pressure doesn't drop below 1.5 (which is where mine differs from other posts as others seems to drop to zero and stop working).

Checked pressure vessel and no water comes out when pin pressed in
Checked pressure relief overflow pipe (ie copper pipe) and no dripping or water escaping (cobwebs are still inside)

C/H and H/W works fine everytime. Pressure increase only noticed the last few weeks and was serviced only a few months ago and every year since new (approx 11 years old now).

Could this still be the pressure vessel not having enough air in? (haven't checked actual pressure in tbh). or something else?

Thanks

 

[Burnerman]

The air pressure in the expansion vessel needs to be checked - but that can only be accurately done when the thing is depressurised. Kick off at about 12 psi if you don't know the exact figure.
John

 

[thewigster1976]

Thanks John for the speedy reply.

Must admit i was planning to redo a section of plumping up in the loft sometime soon so i can put floor boards down so i will be depressurising the system at that point - so may combine both (pressure vessel check first).

Hopefully it wont be too bad to re-pressurise after disturbing some of the plumbing.

 

[MANDATE]

Well in your case the PRV has not been opened so pressure returns to the initial pressure.
PRVs are set to open at 3bar so you're on the brink of it opening I would think.
Once opened and reseated they seldom seal correctly, sediment gets trapped on the sealing face and leaves you with a small leak.

I would bleed a radiator and reduce the initial pressure to around 1bar bringing the 3bar down to 2.5bar

 

[thewigster1976]

Thanks Mandate - have reduced the pressure to 1 bar (via a rad) until the weekend when i can test the pressure vessel some more as per burnerman's suggestion.