Caution: Unplug any coffee maker before cleaning or repairing it. If a percolator is immersible, return it to the manufacturer for repair.
Start your brew with cold water. Prevent coffee grounds from falling into the perk tube by covering its top with your finger when filling the basket. If the coffee tastes bitter, clean the coffee maker by running a solution of 8 cups of water and 2 teaspoons of baking soda through the cycle.
If a percolator makes weak coffee or only warms the water, examine the perk tube and the valve or the ceramic sleeve. Poke any lodged grounds from them with a pipe cleaner. If the perk tube is bent or the ceramic sleeve is cracked or broken, replace it.
If there’s still a problem, the main heating element or the thermostat may be at fault. Each must be replaced by a service center, but you can check them yourself. To get at them, pull the knob from the strength-selector arm and unscrew any screws in the base. Inside there may be an enclosed heating element containing the main heater and the warming element, or the two heaters maybe separate and visible. You’ll also find a thermostat and/or possibly a fusible link.
Always detach the wire from one side of any component before checking it with a continuity tester. Test a separate main heating element or an enclosed one by touching its terminals with a continuity tester; the bulb should light. Test the thermostat similarly, with the strength selector, if there is one,
If the percolator doesn’t heat in a working receptacle, check the cord. If the cord is all right, check the terminal pins; if they are pitted or dirty, smooth them with fine emery cloth. If they are loose, tighten their hex nuts; if they are broken, replace them. If the percolator still doesn’t work, test the main heating element as above.
If the coffee doesn’t stay hot after perking, check the leads of the detached warming element with a continuity tester. If the tester doesn’t light, replace the element; replace any gaskets too. If the element is all right, test the thermostat as above.
Reassemble the components. Make sure that the circuitry is not grounded to the pot: make a continuity test from a terminal to the pot; if the bulb doesn’t light, everything is OK. Drip coffee makers All drip machines have the same essential components: a main heating element, a warming element beneath the pot, a fusible link, a thermostat, and one or two switches. Access is usually gained by removing the back cover plate. On a gravity-feed model, you lift a spring clip and slide out the tank and main heating element. On a pump type, remove the screws.
If the coffee maker doesn’t work in a working receptacle, check the cord. If that’s not the problem, check the main heating element with a continuity tester. Similarly, take out and check the switch, fuse, and thermostat. A maker that brews weak coffee usually has a defective thermostat.
If brewed coffee doesn’t stay warm, the warming element and the switch may be at fault. Unscrew the base plate to release the warming plate, inside of which is an insulated wire heating element (or fine wires on a mica card). Take it out and check it with a continuity tester; check the switch too.
Mineral deposits build up in the water channels of pump-feed drip coffee makers. Once a month run a quart of half vinegar, half water solution (or one recommended in the owner’s manual) through a brewing cycle, followed by 2 quarts of plain water. Use a toothpick to clean residue from the drip tube or dribble notch.