How To Check Water Heater Thermostat

How To Check Water Heater Thermostat

The thermostat is a vital component of your water heater.

Different temperatures of hot water are required for different purposes. For instance, the temperature of the water running through your heating is likely to be different to that of your shower.

The  thermostat in your water heater exists to control and adjust the temperature of the water in your home, tailoring it to your needs. 

How Does An Electric Water Heater Work?

At the most basic level, an electric water heater consists of 3 separate elements.

These are a heating element, a thermostat, and a switch. The thermostat acts as a monitor for the water temperature.

When the temperature is too low it sends an electrical signal to the heating element, triggering it to turn on and heat up the water.

If the temperature rises too high then the thermostat will send a signal to the heating element to deactivate. 

The thermostat is held through the use of a clip into the water tank. It must be submerged underneath the upper level of the water or the thermostat will be inefficient.

The electrical currents sent by the thermostat to the heating element are converted into heat, in turn, heating the water contained within the tank. 

The switch is part of the system used to limit the temperature the water reaches.

When the water reaches temperatures of 120 degrees Fahrenheit or above, the switch will flip and the heating element will deactivate. 

What’s The Difference Between A Single And Dual Element Water Heater?

A single element water heater is the one described above. It only has one thermostat and one heating element, and these heaters are typically smaller in size.

A dual element heater has 2 thermostats and 2 heating elements, and this is the most common style of electric water heaters. These heaters have a top and a bottom, containing a thermostat and a heating element each. 

The top region’s heating element is controlled by the upper thermostat and will contain a high limit switch. This is used as the primary thermostat.

The switch will flip when temperatures exceed 170 degrees Fahrenheit. The lower region is primarily used to detect changes in the water temperature. 

The upper thermostat will send 240 V of electrical currents to the heating element if it detects water temperatures below the set point.

When the temperature is high enough then the power is sent to the lower thermostat, and in turn, the lower heating element. 

How Do You Know If Your Water Heater Thermostat Is Damaged?

The most obvious symptom of a damaged thermostat will be if your hot water tap runs cold.

There is a way of differentiating between a damaged upper and lower thermostat. If the water runs cold from the get go, then the issue is likely to be with the upper thermostat.

If the water initially runs hot and then cools, the problem is more likely to be with the lower thermostat. 

If your water temperature varies as the taps are turned on, this could be due to a faulty thermostat. You should check the settings to ensure that it is set to the correct temperature.

If you think that the thermostat is moving independently of you, we suggest using a permanent marker or some electrical tape to monitor this.

If after this your water temperature still fluctuates through use, the issue is likely due to a defective heating element.

If you are unsure of what is wrong with your water heater, we recommend contacting a qualified professional.

They will have all the correct information and gear available to check out your water heater and fix any issues they discover.

How Do You Check Your Water Heater Thermostat?

In order to do this properly, you will need 2 types of screwdriver (Philips and flathead) as well as a multimeter (also known as a volt-ohm meter). This is a small, handheld device that measures a variety of electrical impulses.

The first step is to turn off the power at the circuit breaker. You should also switch off the hot water supply at this point. 

You should then begin to open up the thermostat access panels using your flathead screwdriver. You will then be greeted with a layer of insulation materials. It is a matter of personal preference whether you remove it completely or just bend it out of the way.

You will then notice a piece of plastic that is covering the heating element and thermostat.

This is a protective safety guard designed to protect you. You will need to remove it to check the thermostat, but just be careful.

We advise using masking or electrical tape to keep the insulator smooth. Take a lot of care to not pull out any of the wiring. 

You should then turn your attention to the high limit switch button. This is often red in color, and you are looking to see if it has tripped within the system.

Common reasons for this switch to flip are the failure of one or more heating elements, the thermostat contacts have fused shut, or if the thermostat is not adequately calibrated.

You will then need to grab your Philips head screwdriver and use this to disconnect the wires that enter each terminal of your heater. 

If you have a dual element water heater, begin with the upper thermostat. Set the temperature as high as it goes. At the same time, turn your multimeter scale to the RX1 setting. 

Set the water meter to the lowest resistance (often around 200 ohms). As you do  this, you will hear a click. Attach the black multimeter probe to the left screw terminal, and the red one to the other.

Take your reading and make a note of the result. If the meter reads 0, your thermostat is working correctly. 

Repeat this process on the right hand side. Again, you are looking for a meter reading of 0. Once you have done both sides of the upper thermostat, do the same for the lower thermostat. 

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