Hot Water Heater Thermostats – How to Replace Them

Hot Water Heater Thermostats – How to Replace Them
May 10, 2012 Lorelie
Hot Water Heater Thermostats

Hot Water Heater Thermostats Proper Replacement

Hot water heater thermostats are a kind of adjustable thermostats that are used to control the temperature of the outgoing hot water.  Below is a review of two of the most common types of water heating residential appliances – gas and electric.

Both gas and electric water heating residential appliances will contain at least one thermostat in order to operate the heater and one high limit switch in order to protect the unit from any excessive temperature.

For different applications, different hot water temperatures are needed.  The hot water is normally needed for showers, clothes washing, dishwashing, etc. and these day-to-day activities are some of the reasons why you use a hot water heater thermostat, in order to set and/or adjust the temperature.

Generally, the temperature range on both gas and electric water heaters differs, but one common thing about them is that they both have thermostats that are factory pre-set, which is usually at 120 F, so as to protect its users from hot scalding water.

It is very important to know that if an individual is exposed to hot water of about 120 F or 49 C, it takes more than 5 minutes to experience burns; if about 130 F, it takes less than 30 seconds; and if the temperature is about 160 F, it takes less than a second to experience burns.

Take note that there are some ways on how to protect yourself and others from accidental burns.  Simply install temperature-limiting valves that connect to faucets in order to limit or restrict hot water, or install a mixing valve in order to minimize the hot water temperature, by means of mixing hot and cold water.

Hot Water Heater Thermostats on Gas Appliances

On gas water heaters, when the incoming cold water activates the thermostat, the gas then flows to the main burner.  By the time the water inside the tank reaches the set temperature, the thermostat then interrupts the gas flow to the main burner.

The residential gas water heaters normally operate within a temperature range of 80 F to 160 F wherein the high-limit safety device opens at about 195 F (on the AO Smith, for instance).

Do remember that even if the thermostat is set to 120 F, the heater may potentially shut off at about 110 or 130 F.  This is due to the fact that the unit depends on the accuracy (+/-10 F tolerance) of the metal rod that is immersed inside of the tank to measure the temperature.

Hot water heater thermostats on gas appliances are actually part of the gas control valve assembly.  The thermostat knob is typically situated at the front of the gas valve.  Its purpose is to control the water temperature and during the process of lighting the pilot and the main burner.  The temperature dial possesses markings, and by turning it counterclockwise, you can increase the temperature setting.

Prior to performing any maintenance on your gas water heater, do remember to turn the temperature dial on its lowest setting.

Take note that the lowest thermostat setting is highly recommended to use during low-demand circumstances.  This way, you can reduce your energy losses during cold days and this also prevents the tank from freezing.

Hot Water Heater Thermostats on Electric Appliances

Electric water heaters are normally equipped with 2 adjustable thermostats, one on each heating element (in case the water heater has two).

The temperature range on residential electric water heater units is normally from 90 F to 150 F with a high limit of about 170 F.  The high-limit switch (ECO) is situated in the exact same place as that of the upper thermostat, has a manual reset (for instance, the AO Smith) and it is meant to shut down the unit if extremely high water temperature occurs (in this case, above 170 F).

The electric water heater thermostats are surface mounted, normally installed into a bracket which holds the element against the side of the tank.  The thermostat’s back surface is in full contact with the tank, thus it responds to the tank surface’s temperature change.

When you are adjusting the thermostat on your electric hot water heater, it is advised that you set both thermostats to about the exact same temperature, or simply set the top element to a slightly lower temperature, so the bottommost element activates first.

How to set the temperature of the water heater via thermostat adjustment

Below are the steps on how to properly change the temperature setting on electric water heaters:

  • Only adjust the thermostat on an electric water heater when the power is off.  Disconnect all power sources to the water heater by means of opening the switch on the fuse box or the main circuit breaker.
  • Take out the access panel, cover and fold the insulation away from the controls in order to clear the way to the controls.
  • With the screwdriver, rotate the adjustment knob to the desired position (temperature).
  • Put back the cover, access panel and insulation.  Turn on the electrical supply and the water heater.

How to replace thermostats on electric water heaters

A thermostat is not that expensive, which is why fixing a thermostat on a hot water heater is not actually recommended. Below are steps on how to replace a thermostat on an electric water heater:

  • Turn off the electric power of the water heater.
  • Take off the front panel door and then fold up the insulation pad.
  • Unclip the thermostat from its bracket.
  • Disconnect the wires from the thermostat.  For proper re-connection to the new element, do label the wires.
  • Take out the water heater thermostat.
  • Install the new thermostat into the bracket.
  • Connect the wires to the thermostat.
  • Set the thermostat to the original temperature setting.
  • Put back the removed elements.
  • Turn on the power to the water heater.

It is highly advised that you check, clean or replace the heating elements as well.  When going to bring the thermostat back, ensure that it stays firmly against the tank surface.  Inside the access cover, you will find a wire diagram.  Use that to properly reconnect the wires to the thermostat.

If in case your electric water heater has two heating elements and two thermostats,  keep in mind that the lower ones will operate more frequently, have more chances of exposure to lime buildup, and tend to fail more often than the upper ones.

When on the lookout for water heater thermostats, it is crucial to know the voltage of the water heater or the heating element.  You can easily find it on the back of the element or on the main energy guide label.

Closing Thoughts

One of the primary problems concerning water heater thermostats are: when the hot water is set too low, the hot water is set to a too high temperature, and when there is no hot water at all.

The reasons behind these problems are actually simple – the thermostat is set either too low or too high.  If in case there is no hot water coming out, then that means either the thermostat is not working or the high temperature limit switch turned the unit off.  If in case you are experiencing running water heating with high operation costs, or if the thermostat fails to shut off, all you need to do is to simply replace the water heater thermostat.

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