Worcester Bosch Greenstar Junior 28i CH/pressure problem

Starting 10 days ago, my boiler (fitted Apr 06) repeatedly cuts out. When CH has been off a while pressure is about 1.0, & when it comes on increases up to 3.0, then the display flashes, CH switches from 'timed' to 'off', & the green heating LED flashes once per second (blue fault indicator light stays on). Usually, the display resets after about 3 minutes & CH comes back on, but goes off again sooner (as pressure is already high to start with). Sometimes the CH doesn't come back on – the display either continues to flash, or returns to normal but the CH setting stays in the 'off' position until switched back to ‘timed’.

I’ve seen the error even when CH was off (pressure was 2.5), & when temp control is reduced to 4.5 for lower output (it's usually at the factory default, 6).

CH seems to stay on about 15-20 mins usually, but varies a lot. RF transmitter is ok. Pressing Reset doesn’t seem to help. Any ideas?

This sounds as if it could be your expansion vessel that has lost its pressure.
Get someone out to have a look.

Andy.

The guy who fitted it already took a look New Years eve - he didn't have any ideas. He said he'd get in touch with Worcester Bosch but I don't have much faith in him, so glad of your advice - it's much appreciated. At least I have some idea of what to expect, & judge whether I should get someone in who knows more about boilers than just how to fit them.

Thanks again...