Thetford fridge.

Hello all,
Slight problem with my fridge. Preparing for first trip this year, going next week, and thought I'd check everything out before I go. Everything going well then I tried the fridge. Now, last year it had a new board and display panel fitted under warranty but I don't think I used the van since. It switched on as usual and the display lit to select the power source then went out as you'd expect. The green light was on to show it was working. I pressed the button to select another source but the display would not come on. I thought I'd switch it off and try again but the power light wouldn't go out. I took out the two fuses behind the drivers seat and unplugged the mains lead and it was still on. If I press the system shutdown button it goes out ok and then when I switch system back on the fridge lights up as it should, I can select different sources but when it settles down with green light on it is impossible to switch off again or select another source. I think the on/off button on the fridge seems like it might be the culprit. It feels ok and clicks nicely.  
I'd be grateful for any suggestions at all. 
Many thanks.

(Thetford fridge by the way)