Worcester Highflow 400 Electronic - pressure too high

[MarkJustice]

I had to replace a catridge in a hot water tap and turned off the water supply in order to do so. When I turned the water back on, I noticed the pressure on the boiler was too low. When I opend the filler stop cock, the pressure immediatiely shot up off the end of the scale. I have tried to reduce the pressure by opening the drain cock, but the pressure doesn't change. I guess there must be an air lock somewhere, possibly in the expansion chamber? Any ideas how I get the pressure down?

 

[superdupergasman]

Have you left the filling loop open or have you opened it further rather than shutting it off??

Once properly shut off, drain it off to 1 - 1.5 bar.

Is the pressure up when the heating is on or off??