Truma water heater issues!

[BarrieLow]

Hi I require your expertise. I have a 1998 Abbey vogue 416 gts. Our truma water heater only appears to work on gas but lately it has just stopped heating. When you turn the control dial the little green light no longer comes on (neither does the red light) and the boiler doesn’t fire up. We have done the obvious, made sure the gas is on, the valves are open, the fuses are intact and the flue cover is off. Have checked the manual and it’s not much help. It’s worked all year until now and we haven’t changed anything. I don’t even know where to start looking, please help