water pressure problem, unvented system

[plomero]

I'm trying to sort out a problem with low water pressure at my elderly parent's house where they have an unvented system. I got a plumber in about a month ago who repressurised the system, after which it seemed better. However there still seems to be a problem, which is most noticeable with the shower, which my brother says is alright when you turn it on, but the pressure and temperature gradually go down. We got another plumber in on Friday who said he thought the problem must be with the shower, but I don't see how it could be (it's just a valve isn't it?). And I noticed this morning the cold tap on the basin in the upstairs bathroom was almost down to a trickle, after filling the basin with hot.
My understanding of these systems is that you should get mains pressure on cold throughout, but the weird thing is that the problem seems to be mainly on the cold. The only difference here is that there is a softener, so I don't know if that might be causing a problem? The kitchen cold is still connected directly to the mains and that's fine.
Otherwise, presumably there's a fault on the system somewhere - maybe the pressure reduction valve? Would that affect the pressure on the cold?
I believe these systems require an annual service, so would a service pick up the problem? Also it's been in use for about 20 years, so I don't know if that's well past the expected lifetime?
Thanks

 

[ShaunCorbs]

Hard water area ?

 

[plomero]

Hard water area ?

Yes, but won't the water going into the cylinder be softened?

 

[ShaunCorbs]

Yes, but won't the water going into the cylinder be softened?

Depends if it’s fed via a softener ?

 

[plomero]

Depends if it’s fed via a softener ?

I assume so because the hot water is soft.

 

[ShaunCorbs]

Would suspect the inlet control group best get an unvented qualified person in eg g3

 

[plomero]

Would suspect the inlet control group best get an unvented qualified person in eg g3

Ok, thanks. So does the system affect or control the pressure on the cold taps, as well as the hot?

 

[ShaunCorbs]

Ok, thanks. So does the system affect or control the pressure on the cold taps, as well as the hot?

Yes depending on how’s it’s piped up

 

[Frelon]

Try by-passing the softener! If the output is better then the softener could be the culprit! After 20 years it may need a service, what make is it?

 

[Rtplumb]

I would suggest getting a G3 plumber in to service your unvented cylinder. He/she will be able to diagnose the problem and tell you what the problem is/might be. It could be anything from a blocked filter in the combination valve to a clogged up out let in the cylinder. As a G3 plumber myself I don't like to diagnose unvented cylinder problems online. I like to see the cylinder in situ and run tests.

Get a G3 plumber in.