When cooking is finished the fan usually continues for a period of time too cool oven down and then switch off. Now the oven fan stays on permanently after switching oven off and the only way too stop the fan is to switch cooker off at the mains.
This problem is caused by one of two components, depending on the model, there is a thermal cut in thermostat that keeps the fan running until the unit has cooled down and on some models there is a four wire timing device that keeps the fan running for a specific time after the temperature drops, the fault can only be casued by one of these components.
Smeg Service Engineer
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With a basic microwave there is a minimum of electronics and the fan starts when the oven is switched on and continues working until cooking has finished. In that case the fan is supplied from the timer and the circuit will be simple to check using a multimeter.
The more upmarket microwaves contain a great deal more electronics and the fan will continue to run after cooking has finished until the circuitry has cooled to a predetermined temperature.
In that case the the checking, fault location and rectification is probably completely beyond even most service engineers - who typically would simply replace circuit boards until the fault is cured...
The oven has internal fan at back of oven encircling the element that should get reshot when stat turned up high. Also there is cooling fan under lid to keep the wiring area cool.This should stay on for around ten - fifteen minutes after cooking finished. David "The Famous Forry"
Probably the cooling fan. There is a cabinet thermostat on most ovens these days (Especially wall or underbench models) to keep the cooling fan running after the cooking has finished and oven turned off. This fan will run for a few minutes to cool down the outside of the oven so it doesn't burn / discolour the surrounding cabinet or workbench. If the fan stays on all the time, I would say that the thermostat has probably jammed in the run or on position.
All microwaves do have a "transmitter" tube called a magnetron. It has to put electrical power into microwaves. To do so it gets warm or even hot. As soon as the transmitter is to hot, it must be cooled down. Most of the time it can be cooled without a fan. But as long as the thermostat indicates it is to hot, the system will cool. Even when you switched the system off. Don't unplug the microwave when it is still hot. It could damage the magnetron.
For TOuch Control oven: 1. Press Finish Time touch pad 2.press ^ touch pad until clock displays the required am or pm finish time. 3. Press Cook Period touch pad. 4. Adjust the cooking time as in step 2, using up and down arrow touch pads. (hours and minutes needed to cook food) 5. Press Automatic touch pad. Press Fan touch pad to select fan speed. Red indicating light shows normal speed. 7. Turn oven thermostat to desired setting. 8. Press Keep Warm touch pad if keep warm function is required at end of cooking. 9. At end of cooking time a buzzer will sound for 1 minute and the KEEP WARM cycle will now operate until the meal is ready to be served. 10. To cancel the Automatic cycle, press Manual touch pad and turn oven thermostat off.
For Multifunction oven: 1. Set time of day. 2. Turn Function switch to Finish. 0.00 will be displayed. 3. Turn display switch + to give the required am or pm finish time. (an illuminated bar in the bottom left corner indicates when the clock display is pm). 4. Turn Function switch to Cook then turn Display switch to + till desired cooking period is displayed (hours and minutes needed to cook food) 5. Turn Function switch to Auto. The automatic programme is now ready to use. Turn upper oven thermostat to desired setting. If keep warm function is required, turn function switch to Cook (optional)
1. Faulty thermostat. 2. Faulty thermal cut out switch. (controls power to cooling fan). 3. Faulty cooling fan (not fan inside oven).
Test thermostat by setting thermostat to low temperature like 60 oC. If oven gets much hotter then its a faulty thermostat. To test cooling fan and thermal switch take oven out and remove top or rear panels to expose components. When oven gets hot the cooling fan should turn on. If it doesn't then check to see if there is a mains voltage present. If mains current exist but fan is not turnig then replace fan. If mains voltage is not present then its the thermal switch.