Where can I buy only the magnet for the door sensor?

Any magnet that works will do the job. All you are using it for is to close a switch.

buy a replacement and just use the magnet part
for a
Magnetic Door Window Contact Sensor Alarm Reed Switch Security Burglar Alarm
lots of places sell them
google search on
Magnetic Door Window Contact Sensor Alarm Reed Switch Security Burglar Alarm
or go to an electronics store in what every country you live in and ask for
Magnetic Door Window Contact Sensor Alarm Reed Switch Security Burglar Alarm

Hi , to test door magnet put close a small piece of iron, it should be attracted, this sensor is very rare to fail, possible the door sensor is faulty, this is a magnetic switch, to test it, you can put together both wires going to it (doing a short circuit to sensor), if the cable is OK the indicator of an open door should turn off and system will go to ready state. If all this happens, you need to change door sensor.

HELLO, I just found out that the door error might be caused by a sensor not realizing the magnet at the plastic cover. You can either change the magnet or simply "power it up" by another magnet. The magnet is located on the plastic top/cover. Hope this is helpful.

If your fridge has a manual door switch which gets pushed when door is closed, then you can tape up the door switch.
Some fridges have a magnetic sensor, so you can cover the sensor with a magnet.
Failing those you can remove the light globe.

The magnet needs to be less than about 1/4" from the light when the door is closed to activate the magnetic switch in the light and turn the light off. Fix the light to the frame or wall inside the cupboard and the magnet to the door.

most GBX shredders have a magnetic "reed" type switch inside the shredder head that is actuated by a magnet on your door. have you recently lost the magnetic catch on your door? if you have lost it and have access to a strong magnet, you should be able to open door and move magnet around on front side of shredder head and see the light go out. if magnetic catch is on door, then perhaps your door is misaligned in such a way as to not energize the switch.

good luck,
razors

The machine has a small magnet on the front of the lid. There is a sensor (Hall Effect probably) in the electronics block that senses if the magnet is there (lid closed) or not there (lid open). They aren't that well attached and seem to fall off and wind up in the wash, which means they get lost when the washing is being hung out.
The machine will not start without the lid closed you get a dE error code which means the lid is not shut. You can trick it temporarily by putting a small round magnet inside the front housing if you don't have a proper replacement, as the real one needs to be quite strong. Not sure what they cost, my husband just did the 'trick' to our daughters machine, but a small button magnet wasn't strong enough to trip the sensor from the lid position, he had to stick it right next to the sensor.
Shouldn't be that dear, you can buy blocks of very powerful neodymium magnets in varying sizes for under ten dollars.

There really is a sensor magnet that is necessary for door lock mechanism to work. Not sure about service call charge, but if it works the he did fix it anyway

I still had the gas door, so I went to Home Depot and bought 4 round heavy duty magnets and secured them with epoxy inside the four corners of the gas door and body of the car around the fill area. Now my gas door just attached by magnets instead of a hinge.