Cold water pressure valve not working

[bees]

I have a Worcester Bosch RD 532i gas condensing boiler, which is only two years old.
The cold water pressure has dropped to around 0.5 bar and the pump has run dry so no hot water is being produced (if the boiler is switched off and on again hot water is produced temporarily).
When I open the cold water valve no water flows into the boiler.
There doesn't seem to be any obvious leaks.
The problem has persisted for just over a week.

Any advice as to why the value might not be working much appreciated.

 

[Gasguru]

The pressure at 0.5 bar will not damage the pump so if its run dry it must have a significant amount of trapped air within it.

It normally takes a significant amount of running at zero pressure with the boiler at the highest point to kill off a pump.

Does the filling loop have two valves? Are both open.

Perhaps your mains pressure is only 0.5 bar (not uncommon) or the pressure gauge is inaccurate (ie reading low).

What type of filling loop valve is it - the old types with the white handles can appear to turn but the valve threads sieze up.