Glow Worm Compact 100E - Water Heating Problems

[atri]

I have a glow worm compact 100E that shows the gas pressure exactly 2.

Sequence of events:
1) I switch on taps for hot water.
2) The "SANITARY DEMAND" light takes 10 seconds to glow.
3) Once it starts glowing then "BURNER IGNITION" light takes 5 seconds to glow.
4) "BURNER runs for 5 seconds then the red light "BOILER LOCKOUT" gets glowed.
5) I press the "RESET BUTTON" then the red light is off.
6) During all the above "SANITARY DEMAND" light is fluctuating with a sequence of clicking sounds OR
7) During all the above "BURNER IGNITION" light is fluctuating with a sequence of clicking sounds

8) If I am lucky then after leaving the hot water tap ON for 5 min and trying all the above, the hot start flowing OK for good time any further trouble

all the had to done every time, I switch on hot water tap.

Please note that when I leave the boiler on "WINTER SETTINGS" i.e. both water and radiator ON then all is OK.

Please help.