Worcester Greenstar 28i over pressure

[stevejs]

We have a 4 year old Worcester Greenstar 28i boiler that we tried the CH on for the first time this winter the night before last - it has been supplying hot water fine since fitting
The pressure gauge rose up to 3.5 bar before I chicken out and killed it
My questions are what is wrong with the boiler and is there a failsafe pressure release valve that should have opened at what pressure and where does the excess water drain to ?

 

[Burnerman]

The pressure release valve should lift at 3 bar, and the excess water should discharge through a pipe outside - usually turned back in on itself towards the wall.
I would imagine that the air pressure in the expansion vessel could be low....
John

 

[stevejs]

Which means a new expansion vessel ?
or is it somehow possible to top up the air pressure ?

 

[Burnerman]

To check the EV Steve, there should be no pressure in the water system at all. Bleed the pressure out from a rad valve - it takes a while but its foolproof. Leave the rad valve open until later.
Then, put a car type tyre gauge on the schrader valve at the top of the EV and check that its around 10 psi (for a guide).
Pump it up with air from a foot pump or similar, close the rad valve and repressurise the system via the filling loop.
If water is present when you check the EV's pressure, then its certainly goosed.
John

 

[stevejs]

To check the EV Steve, there should be no pressure in the water system at all. Bleed the pressure out from a rad valve - it takes a while but its foolproof. Leave the rad valve open until later.
Then, put a car type tyre gauge on the schrader valve at the top of the EV and check that its around 10 psi (for a guide).
Pump it up with air from a foot pump or similar, close the rad valve and repressurise the system via the filling loop.
If water is present when you check the EV's pressure, then its certainly goosed.
John

If we need a new EV - How much are they ?