Why is my Worcester 28i junior tripping out all the time?

I have similar problems and the more I read the more I think there is a common fault with these Worcester 28i boilers.
1st problem is that when central heating is on and I turn on a hot water tap the gas just goes off and the alarm light flashes - this happens quite a lot but not all the time.
More recently we had low mains pressure & the boiler pressure dropped - this shouldn't happen as the two shouldn't be related (the fill tap is closed).
I've also noticed that the boiler pressure vaires from day to day.
I saw that someone had to replace a diaphragm after three years - does anyone know if a faulty one may show the problems described? Is there anyway the heat exchanger could have some kind of hole in it?
Any help greatly appreceated.

Adam Brown
January 2009

the expansion vessel, behind the boiler at the top and is red, has a valve the same as car tyre the boiler should be drained perhaps through pressure relief valve, and the expansion vessel should be pumped to manufacturers pressure possible 1 bar. then close pressure relief and re-charge system pressure to minimum 1 bar this should rectify problem. if it should re-occur relatively soon you will need to replace expansion vessel. good luck hope this helps.

heater
January 2009