The microwave lights up, the fan and turntable run and the timer counts down, but the food comes out stone cold.
Usually: Almost always a failure on the high-voltage side: a shorted or open magnetron, a failed high-voltage diode, or a capacitor that has dropped out of tolerance.
On the visit: We run a timed water test to confirm no heat is being produced, discharge the capacitor safely, then test the diode, capacitor, transformer and magnetron in turn so the right part is replaced rather than the obvious one.
The plate sits still while the food cooks, so one side comes out hot and the other is still frozen.
Usually: Usually a seized or burnt-out turntable motor, a stripped drive coupler on the cavity floor, or a roller ring that has collapsed and jammed the plate against the base.
On the visit: We lift the plate and ring, turn the coupler by hand to see where the resistance is, and check the motor for drive and continuity. Motor, coupler or ring is replaced as the test shows.
The microwave is completely dead. No display, no light, nothing when the door is opened.
Usually: Typically the internal line fuse has ruptured, and on a built-in that is often triggered by an interlock monitor switch reacting to a door switch that has failed out of sequence.
On the visit: We slide the unit out, check the supply at the housing first, then test the line fuse, thermal cut-outs and the switch sequence so the cause is corrected and the replacement fuse is not simply blown again.
The unit only starts if the door is pushed or slammed, or it cuts out partway through a programme.
Usually: Worn door interlock switches, or latch hooks and the door itself dropping slightly on their mountings so the switches no longer operate in the correct order.
On the visit: We test each interlock switch for correct make and break, check the latch hooks for wear and reset the door alignment in the housing. Switches are replaced as a set where they have worn together.
Some buttons on the touch panel do nothing, or the microwave starts a programme on its own.
Usually: A membrane keypad that has lost contact through steam ingress and heat from the oven underneath, or a control board with a failing track behind the ribbon connector.
On the visit: We test the keypad response and the ribbon into the board to work out which of the two is at fault, since a membrane and a board are very different repairs. The failed one is quoted before we order it.
The cooling fan is far louder than it used to be, or it keeps running long after the cooking has finished.
Usually: Dry fan bearings, or a housing whose vents have been blocked by dust and cabinet trim so the cavity stays hot and the fan run-on keeps being retriggered by the thermostat.
On the visit: We check the fan for bearing noise and free rotation, clear the vent path, and confirm the housing has the clearance the unit needs. Where the fan itself has failed, it is quoted and changed.
On a combination model the microwave function works, but the grill or fan-oven side stays cold.
Usually: Usually an open-circuit grill element or convection element, though it can be the relay on the control board that switches that circuit rather than the element itself.
On the visit: We test each element for continuity and check whether the board is actually calling for it, so an element is not fitted to a machine whose relay is the real fault. The part is quoted before fitting.