Thermostat for a water heater: how to repair or replace

The thermostat for a water heater works on the principle of a thermometer – it measures the temperature. Why this is necessary and what threatens the breakdown of the element, read in our publication.

The device and principle of operation of the thermostat

How does the device work? On the control panel you set the heating values. As soon as the water reaches the set parameters, the temperature sensor is triggered, sending a signal to the control module. The latter gives the command to turn off the heating element.

In storage boilers, the water is constantly warm thanks to the temperature controller. As soon as the indicators decrease, the heating element starts up again and continues heating. Therefore, you can get hot water at any time without a long wait.

In modern models, the thermal relay is equipped with an off button – thermal protection. When the heating element overheats or heats the contents above the specified norm, the protection is activated and the work stops. Otherwise, the heating element will burn out.

Device Diagram:

There are several types of thermostat:

  • Rod – obsolete type, no longer used. It is based on a tube that expands when water is heated. From the extension, the heater switch-off key is triggered. This design was abandoned due to its inaccuracy. The part was located close to the cold flow intake, so it did not have time to respond to an increase in temperature in time.
  • Capillary. The design is the same, but in this case the tube contains a liquid that expands and actuates the heating element relay. The error is 3-4 degrees.
  • Electronic. The most accurate of all sensors. Equipped with protection against switching on without water.

For the electric water heater, regulators have been developed:

  • Mechanical and electronic (overhead and built-in, respectively). Mechanical ones are triggered by the expansion of bimetallic plates, electronic ones are triggered by a sensor signal.
  • Programmable and mechanical. The first requires the installation of the necessary indicators, the latter are triggered by boiling or when the maximum manually set temperature is reached.

The boiler stopped heating or, on the contrary, overheats the water? The thermostat is checked first.

How to do DIY repairs

If possible, the element can be repaired or a new one installed.

How to remove the thermostat:

  • Disconnect the equipment from the network.
  • Shut off the water supply.
  • Drain the contents of the tank. To do this, you can use a special valve. Why you need a safety valve, read in a separate article.
  • Dismantle the heating element. To do this, unscrew the nuts and bolts of the flange, remove it from the body.
  • The thermostat is usually located at or near the base of the heater.
  • Disconnect the wiring and remove the sensor from the base.

In the case of a mechanical model, clean bimetallic plates from oxidation. To do this, soak a piece of cloth in alcohol, wipe the plates. If the oxidation has spread greatly, then clean with fine sandpaper.

This must be done carefully so as not to touch the sensor contacts.

Due to power surges, the NC contact could stick. To adjust, carefully detach it from the body, clean the problem area. Normally, the contact should be in the socket automatically.

How to repair a contact if it doesn’t work:

  • Remove the part completely from the housing.
  • Clean its surface, as well as the seat.
  • If the contact does not turn on after cleaning, place an insulating tape underneath.
  • Reinstall the stem.
  • Assemble the body.

When the regulator needs to be replaced

It makes no sense to repair if:

  • The copper tube has fallen into disrepair.
  • The electronics are out of order.
  • The element burned out during a power surge.

But how in practice to make sure that the thermal relay is faulty? This can be checked with a multimeter.

  • Set the multimeter to resistance measurement mode, as shown in the picture:
  • Attach the probes to the contacts of the part.
  • Look at the scoreboard. With infinite resistance, the thermostat cannot be restored, a replacement is needed.
  • Shows resistance? Do this: set the multimeter to the minimum value. Heat the thermostat tube with a lighter. If it is working, the resistance will increase and the protective relay will work.

If you are convinced of a malfunction, it is important to choose the right product for replacement. How to do it? It is best to take the old regulator and go to the store with it to purchase an analogue. Or write down the serial number that is on each product.

What to look for:

  • fastening method.
  • The size.
  • Voltage.
  • Additional functions.

The parameters must match those indicated in the passport for the boiler.

If you are not strong in repair, then you can call the master for a replacement.

Remember safety precautions and watch videos on the topic:

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