Door switches can have problems because they are often located in very hot areas of the equipment.
Our newer door switch is metal with two halves. On front loaders it is mounted on the front with one half on each door. Top loaders have the switch mounted on the side near the back corner. If the “Interlocks Closed” light is not turning on when the door is closed, and there is no error code on the Watlow, the door switch may be faulty. The first thing to try is swapping two wires of the door switch. The cable has several unsused wires inside it. We normally use Black, White, Red, and Blue. Strip back the cable to reveal more wires. Locate where the Red and Blue wires go, and replace them with the green and yellow wires. This may make the door switch work again. If not, you’ll likely need a new door switch.
Also make sure the doors are fitting tight and that the gaskets are not wearing out. These can let heat leak out causing door switches to go bad faster.
Our older door switches have either a spring toggle switch, or a push button. A bolt or bar on the lid or door presses this button or switch. Try adjusting the bolt or bar to press more on the switch, it may have shifted over the years and stopped pressing enough. If the switch will no longer trip at all, shut off the power and remove the cover of the switch to see if a wire has come loose. Also check inside the control panel to see if a wire has come loose there.