Panasonic Microwave Combi Oven - convection...

Question

Panasonic NN750WB.
Fairly subtle problem - the convection function (on its own, in combination with micorwave or on 'turbo bake' setting) doesn't activate with the program timer. Convection works on pre-heat i.e. the elements come on and bring the oven up to temperature but when a time is programmed in they stop activating. The grill function works on the timer and uses the same elements. Have taken the outer case off and can't see any obvious dodgy connections.