WB Greenstar 28i Junior, about 5 yrs old.
After about 5 minutes in the shower the boiler goes into lockout with red light flashing once a second, blue light flashing once for every 2 flashes of the red, and water goes cold.
Pressing the reset button brings it back until next time. Doesn't do it every time but getting more and more frequent, with time to lockout getting shorter.
Pressure in heating loop at ~1.5 bar.
Googling shows this is a common complaint but doesn't offer much in the way of help. There seem to be several variants of this model with no common fix for the fault.
Might be relevant: the boiler had two replacement heat exchangers under warranty but has been OK for the past ~3yrs.
Any ideas, please?