Looks like it's ok now
I pulled the fridge out and found one connection from the ign switch to the igniter unit was loose. But as I pulled it off to tighten it I clumsily yanked thye other two wires off as the have been loose too (that's my excuse anyway

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After some faffing around with a 12v test screwdriver lamp the only way I could get it to 'tick' was by holding my tester onto a terminal. And I note that the negative supply is also live, making the gas valve carry 12 v too as it connects to its metal holding bracket.
Anyway, the schematic doesn't show how the vernitron unit is wired some I can only get it to work by putting an earth lead from the ground on the vernitron unit and all works but the switch itself doesn't light as it ticks but I can live with that. Also, its turning itself off once the pilot gets hot so I'm assuming all is well now. I still dont understand why an extra earth has fixed it as I removwd and cleaned all the earths on the back of the fridge but hey ho, it works now.
Thanks for your help
