What is a solenoid?

A solenoid is a coil of wire that becomes a magnet when energised, pulling a plunger to open a valve or throw a latch. Water inlet valves, gas dryer burner valves, detergent dispensers and door locks all use them. Solenoids typically fail either open-circuit or by weakening with heat — the latter producing the frustrating fault that works cold and quits once the machine warms up.