Vokera boiler,,,,,relief,,,no hot hose down.? my linea combi boiler is driving me crazy. c/h is fine, but...

my linea combi boiler is driving me crazy. c/h is fine, but hot water go cold after starting to warm up. burner go on, then switches bad after a couple of seconds, showing error 3.
british gas come out and replaced pcb,thermistor,return valve, excell service tools, problem still continues. is the boiler posessed, or is the engineer trying to hoodwink me.
Cast Iron Bath?
Answers:    We have the same problem near the same boiler. It get so bad the neighbours thought my wife be havng an affair with the man from British Gas. It go on for two years, I think the entire boiler must own been replaced over that time.

We never did attain to the bottom of it - solved the problem by selling the house.
How much dampen do I have need of...
an 03 fault on a vokera linea is indicating a culpability with the devotee or flue.the flue venturi which operates the heavens pressure switch is probably blocked.it works fine on heating mode,but when on hot hose the boiler burns at a higher rate,which puts the flue system lower than more pressure causing the pressure switch to switch past its sell-by date.its a common glitch.