Expansion Vessel - right capacity?

[Sasso]

Hi, I have a Potterton Prima B system boiler. The hot water cylinder is the kind where it has the combined F+E on the top section of the cylinder and the cylinder has a small (o.5 litre) expansion vessel on it by the 2 port valve. However, the expansion vessel started leaking a year ago, I got a direct replacement and that only lasted a few months before leaking. I am wondering if the capacity is too small and the pressure is causing it to leak? Should I go for a larger vessel next time? Or maybe I am just unlucky and the vessels are not much good....
Thanks

 

[ChrisR]

0.5 lites ??
If the boiler system is sealed, you need something like several litres, half a dozen at least.
If the heating system has its own header tank you don't need a pressure/expansion vessel at all.

 

[seco services]

Sounds like your talking about a shock arrestor for water hammer.

 

[picasso]

I wonder if the op has a thermal store, any chance of a photo ?

 

[Agile]

Is the Prima designated for use on a sealed system?

 

[Sasso]

Hi folks, thanks for the responses, here is a pic of the thing that is leaking...

Untitled

• Sasso
• 16 Jul 2011
• 1

 

[jerholdsworth]

a photo showing the complete cylinder would help these guys.

 

[Sasso]

heres a pic of the whole cylinder, thanks

Untitled

• Sasso
• 17 Jul 2011
• 1

 

[gasafengineer]

Maybe pressure reducing valve is faulty causing excessive water pressure to vessel , what is the max pressure rating for the vessel?

 

[Sasso]

The pressure vessel reads 'maximum working pressure is 10 Bar' and the pressure reducing valve - assumng I am looking at the right component - rads 2.5 bar max. thanks

 

[steve32]

The expansion vessel should be fitted upright not sideways. (schrader valve at the top)
This is the most likely cause of it leaking.
What was the charge pressure when it was fitted it should be 1 bar below water mains standing pressure.
The units are charged to approx 2-3 bar you adjust it when fitting and check the pressure yearly.

 

[MeldrewsMate]

That looks like a shock arrestor (damper) on the cold mains feed to the cylinder and the combined header tank ballcock. It also looks like it's a heatstore, the cold mains tees-off just below the shock arrestor to what looks like a mixing valve....do you adjust the hot water temperature here?

In any case it seems that the expansion vessel is being damaged, it has already been suggested that the pressure reducing valve may be faulty. There should be a pressure gauge port on it. so you can check the output pressure.

MM