Seen a thread here from 2015 similar to mine, help needed, i got a worcester 28i junior combi, cannot get c h gauge no lower than 2bar, started after street mains got turned off, i had to drain and refill c h system, run ch after about 10 seconds banging noises along pipework dor around 30secs then calms down, bled c h again, no good, removed all rads, pressure hosed them, (loadsa black muck), refilled and same, theonly way i can lower pressure in c h is by mains stopcock then i have low tap pressure, or i turn on a tap and that lowers it to 1 bar and holds it there. there was no plumbing work done, suggested sludge had moved to heat exchanger, noise does seem to be coming from centre of boiler. Anyways just bled a radiator upstairs, nothing but air, when nothing else came out i check boiler gauge, zero, i link fed system to 2bar, re bled all radiators, wont go below 2 bar to 2 1/4 bar, isolated mixer taps and shower mixed via inline isolators, turn ch on and 10 secs later banging pipes, gauge fluctuating all over the place, bout 40secs later all calms down for now until boiler kicks in again when via thermostat? Puzzled, so am i, i will be getting in a local plumber even if its for a diagnostic, im just inquisitive as to why, like i said all ok till mains outside turned off, coincidence? I got short videos too while doing checks.