Water heater Thermostat | How Does it work?

Heating of water can consume a lot of electricity. It is in the fitness of things that you do your basics right. In order to conserve electrical energy, you need to maintain the water at the right temperature.

Thermostats can allow you to do that. The modern-day geysers come equipped with such thermostats instead of immersion rods.

Thermostat – The Concept

A water heater thermostat is a safety arrangement because it does not allow the water to get heated beyond the set temperature. It works by switching off the power supply to maintain the water temperature at the desired level. Thus, it prevents the water from reaching high temperatures that could cause accidental burn injuries. Besides, it saves power. 

Read: Latest water heater technologies

Thermostat – Location

In India, you get of water heaters, one where the thermostat controls are visible and the other where they are not. In the former type, you have the facility to change the temperature settings as required.

The latter category does not have this facility. Such thermostats have a pre-defined setting of temperature at around 550C to 600C. These water heaters have red and green light settings to indicate whether the heating process is on or off.

How many thermostats does a water heater have?

The water heater has two thermostats. The upper heat thermostat controls the upper-temperature level. So, it does not allow the water to get hot beyond the upper set temperature. On the other hand, the lower heat thermostat restarts power consumption when the water temperature goes below the lower set temperature. Thus, both thermostats work together to maintain optimum water temperatures in the appliance.

What happens when the thermostats fail?

Water heaters have a reset button called Emergency Cut-Off (ECO) switch. The ECO switch trips if the upper heat thermostat fails. It shuts off the power supply to the geyser and prevents the water from getting overheated. The solution is to replace the thermostat and reset the ECO switch.

Similarly, the geyser does not switch on automatically if the lower heat thermostat fails. So, again, the solution is to replace the thermostat.    

The ideal temperature for water heater

The ideal temperature setting in a water heater is around 50C. Most of the geysers available in the market have a range from 40C to 75C.

It is up to the individual where to maintain the setting in case you have access to the thermostat controls. Remember, that the input water temperature is an important factor.

Your electricity consumption depends on the difference in temperature levels between the input water and thermostat setting.

There is the concept of using solar water heaters in combination with electric geysers as a back-up option. You need this option on cloudy days when the solar power will be at its minimum.

The advantage of using solar water heaters with back-up electric geysers on such days is that it reduces the temperature difference between the input water and thermostat setting. This save you power.

Points to ponder

This part of the article attempts to clear the misconceptions people have about the working of the thermostat.

  • Thermostat does not completely switch off the electricity supply after the water is heated to the desired level. It merely suspends the supply of electricity to the appliance. As soon as the water temperature goes down beyond a certain level, it switches on the supply thereby continuing with the heating process.
  • Many people have the tendency to leave the geyser in the ‘ON’ position at all times believing that the thermostat takes care of the water temperature. Remember the concept of standing loss. Water stored inside the storage tank will lose heat.
  • Under such circumstances, the thermostat starts functioning again. If you leave it in the ‘ON’ position at all times, the water heater will keep working the entire day thereby consuming a lot of unnecessary electricity.

BEE Star Ratings

The important factors affecting the BEE Star rating ratings is the heat loss. In case of other appliances power consumption by the appliances is the principal factor affecting BEE rating. In case of water heaters, the emphasis is on heat loss.

The more the standing loss, the lower is the BEE rating. A 5-star BEE rated water heater will have less heat loss as compared to a 1-star geyser. The thermostat has an important role to play under such circumstances.

Read: Best Water Heaters

Important tips to save electricity

  • Maintain thermostat at medium levels. Do not overheat the water.
  • The size of the geyser is important. Refer to the table provided in one of the earlier blogs and ascertain the right size for your home.
  • A 5-star water heater is always preferable.
  • Switch off the geyser when not in use. The standing loss concept comes into play.
  • Proper insulation is necessary to avoid unnecessary heat loss. This is especially true if the distance between the geyser and the bathroom is longer. There can be transmission loss.
  • guiUse of thermal paint on water heaters can save you power. Our next article deals with this issue.

Use your water geyser wisely. It can serve you for a long time.

Gaurav Arvind
Gaurav Arvind
I am a software engineer by profession but blogger by passion. I have been doing blogging, reviews and writing about products for the past 3 years. I love what I do. If you can't tell me what it's made of, I won't tell you how good it is !


  1. In my water heater there are two option written ..Mains/ Heating….my electrician asking where should he set it on Mains or Heating. What should I say. What is Mains?

  2. can you put a shorter thermostat then the one supplied, original
    stat 17 inches replacement 11 inches (vertical) .

    many thanks keith


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