Glow worm compact 60

Cover off combustion chamber boiler fires up no problem, put the cover on and fan comes on, spark comes on, but no gas, have checked airswitch, flue, fan, board any ideas would be greatly appreciated boiler is circa 2002

"Combustion chamber cover"? Part 24, "retaining plate" or Part 40, "main front panel (inner case)"?

Neither part can affect gas flow to the burner. The manifold bolts to the gas valve and has a jet screwed in at the top that feeds gas to the burner. The manifold is made from 1/2" steel gas pipe.

I have little experience with G-W sealed systems from this generation but I see this has a 2 stage modulating gas valve and no pilot. Ignition is at RHS on main burner and flame detector is via 2 electrodes at LHS. Burner gets a small pilot/ignition gas feed and it will spark until flame is detected at LHS of burner, gas flow will then modulate up for full load.

Check routing and condition of the ignition lead. For each ignition "tick" you should be able to look in the little window part "41" and see a spark between the electrode and the burner. If it ticks but you don't see a spark then it has sparked to ground somewhere else along the ignition lead. Check the condition and correct fitting of the 40mm silicon insulation tubes on the ignition electrode and the 2 flame detector electrodes.