All About Water Heater Resistor: Operation, Maintenance, and Changeover


 – Operation of the water heater resistor

 – Water heater resistance: maintenance and change

 – Price of a water heater resistor

An electric storage water heater is composed of:

 – an enameled and confined tank, maintained under constant pressure;

 – a resistance for a water heater;

 – a thermostat for temperature control;

 – an anti-corrosion system.

The resistance of the water heater is an essential part of your cumulus:

 – It ensures the temperature rise of the water in the tank by transforming electrical energy into thermal energy.

 – It has an electrical connection system at its base.

 – It will scale over time, but it can be cleaned and changed if it is defective.

You can also change other spare parts of the storage water heater in case of a problem:

    • The thermocouple
    • The anode of the water heater
    • The water heater’s safety group

Operation of the Water Heater Resistor

Water heater resistance: two types

There are two types of resistors for water heaters:

 – The entry-level thermoplastic resistance (called an armored water heater):

 ◦ in stainless steel;

 ◦ directly in contact with water;

 ◦ requires regular maintenance because it scales quickly;

 ◦ with a relatively short life span.

 – The soapstone resistance:

 ◦ surrounded by a sheath often enameled, and therefore protected from scaling;

 ◦ more expensive, but with a longer lifespan;

 ◦ can be changed without having to drain the tank.

Water heater resistor: operation

The inner wire of the water heater resistor, which is made of a metal mixture, heats up when current flows through it. This wire is surrounded by insulation that is covered with a protective coating. It is connected to the tank and secured by a ground (yellow/green wire).

Over time, the water heater’s resistance becomes scaled and overheats: its resistive wire is gradually destroyed, the resistance begins to heat less until it does not heat.

Water heater resistance: maintenance and replacement

To service or replace the water heater:

 – In the case of a thermoplastic heater, you must drain the tank completely:

 ◦ which results in a large volume of hot water being wasted;

 ◦ but allows access to the cumulus to descale the tank or change another of the cumulus organs.

 – For a resistor, you can intervene without emptying the tank.

How to clean or change the thermoplastic resistor?

Here is how to dismantle the thermoplastic heating element. Depending on the condition of the water heater, you will either descale it or change it.

Thermal immersion heater: disassembly


  • Turn off the power to the water heater.


    • Turn off the cold water supply to the safety group.
    • Connect a garden hose to the drain valve and place it in the nearest sink.
    • Open the hot water taps at your water points.


    • Remove the resistance held by nuts.
    • Take this opportunity to change the seal at the base plate.


    • Dip the heater in descaler (heated white vinegar does the job very well).
    • Let it work; the time depends on the level of scaling.
    • Check regularly and rub the resistance with a soft wire brush.


  • If it is defective or in terrible condition, replace it.


    • Take the opportunity to clean the tank by removing as much scale as possible, by hand (wear gloves), or scrubbing with a brush.
    • Clean or replace the anode.


    • Rinse the resistor and put it back in place without forgetting the joint.
    • Tighten the nuts on the base plate gradually without crushing the gasket too much.


    • Close the drain valve and tap at your hot water points (leave the one furthest from the water heater open).
    • Open the cold water inlet valve on the safety group.
    • When the water flows from the faucet left open, your tank is full.
    • Turn the water heater back on.

 How do I clean or change the resistor?

Because it is protected from direct contact with the water, the resistor will only become very slightly entangled—limescale deposits on the sheath. If you have to change the soapstone heater, proceed in the same way as the immersion heater, but without draining the tank.

Price of a heater

Here are the indicative prices of the resistances for water heaters.

Price of the water heater resistor


From $60 to $200

From $30 to $100 

You can read more here:

4 Easy Steps to Drain a Gas Water Heater

What Are the Different Forms of Water Heater On The Market