worcester bosch

[steveyboy]

I have recently replaced the expansion vessel, pressure relief valve and filling loop as I had problems with fluctuating pressure and thought this would cure, however water pressure still seems to rise. Boiler is about 7 years old and I can see no signs of leakage. Any help would be appreciated!

 

[oilman]

Nothing odd in that, pressure will rise, but by how much?

With system cold, set the air pressure in the vessel, set the system pressure 0.2 bar higher, then start the boiler. For a two storey house the air pressure should be 0.4 to 0.5 bar. When the system is hot the pressure will rise to 1 to 1.2 bar or so, much higher and the pressure vessel is too small.

 

[sifu]

*IF* the pressure is excessive i.e. more than oilman suggests, then did you check for blockage in the pipe leading to the EV?

 

[steveyboy]

pressure had been rising till pressure relief valve cut in at 3 bar, although all seems well at the moment (touch wood). Another problem had been air in the system, always seems to be the rad nearest the boiler.

Ps - I was told that you never had to pressurise a new expansion vessel?

Thanks for the advice oilman! :

 

[steveyboy]

PPS - Meant to ask the purpose of an Expansion vessel as the manual explains very little on the workings of all the boiler components?

 

[ChrisR]

It has pressurised air (may be nitrogen when new) in it so the water has something to squash when it expands on heating.