How to Fix a Vertical Immersion Heater

Turn off the water supply to the hot water tank by closing the shut-off valve on the water inlet line near the top of the tank.

Locate the breaker switch on the main electrical panel feeding power to the water heater. Trip the breaker switch to the “off” position and secure it to the panel with a strip of masking tape to prevent someone from restoring power while you’re working.

Open a hot water faucet and drain off about a gallon of water to relieve back pressure in the tank.

Remove the cover plate on top of the immersion heater by undoing the securing nut with a nut driver; this will expose the electrical wiring. Take a snapshot of the wiring configuration with a camera phone or digital camera to use later as a reference if necessary.

Touch the prongs of a neon circuit test light to the black or red live connection, and to the white neutral connection on the immersion heater. If the tester does not light up, the circuit is safe to work on; if it lights up, you’ve isolated the wrong breaker switch.

Disconnect the faulty immersion heater by removing the terminal nuts with the nut driver and pulling the wires off the terminal posts.

Squirt a generous amount of penetrating oil into the recess surrounding the immersion heater nut to loosen the threads. This ultra-thin oil is specially formulated to penetrate between locked threads and dissolve rust. Allow 10 to 15 minutes for the oil to work before attempting to remove the heater.

Place an immersion heater wrench -- a large, long-handled ring wrench designed to fit over an immersion heater nut -- over the nut. Press the end of the wrench down with one hand and, with a hammer, deliver one or two sharp blows to the wrench handle in a counterclockwise direction to loosen the treads.

Unscrew the immersion heater and take it out of the tank. Measure the length of the elements and obtain an identical replacement.

Wrap the threads of the replacement immersion heater with a counterclockwise spiral of plumber’s pipe sealing tape. Stretch the tape while doing so to allow it to settle into the threads, then snap the end off and smooth the ragged end of the tape into the threads. Place the large, round sealing washer supplied with the unit over the heater flange. Insert the heater into the tank and start the threads by hand.

Tighten the immersion heater firmly in a clockwise direction with the wrench. Open the water supply shut-off valve on top of the tank. Have a helper open the hot water faucet farthest from the tank to release trapped air in the pipes. Tell him to close the faucet as soon as air stops hissing out, after about 30 seconds, when the trapped air is purged and the hot water supply pipe fills with water.

Check for leaks my examining the immersion heater nut. If water starts seeping out, tighten the immersion heater nut a little further until the leak stops.

Reconnect the wires to the heater by referring to the instructions that came with the unit, or by consulting the snapshot taken earlier. Tighten the terminal nuts securely with the nut driver and replace the electrical cover plate.

Restore power to the water heater by resetting the breaker switch. Wait half an hour before opening a hot water faucet to ensure that the immersion heater is working properly.