If your water heater is taking more than the usual amount of time to heat the water, which then suddenly goes cold after a few minutes, your thermostats are to blame. Thermostats are responsible for controlling the heating elements and ensuring that your water reaches an optimal temperature that’s both comfortable and safe on your skin.
Here, we’ll share a quick guide using which you might be able to fix the problem yourself at home. How to test a water heater thermostat? Let’s find out.
How Many Thermostats Does a Water Heater Have?
Most water heaters have two thermostats, one on the upper region and one on the lower. They each manage one of two heating elements, with the primary responsibility of managing the great falling on the upper one. The upper thermostat not only controls its partner, but is also connected to the high-limit switch that prevents water from getting dangerously hot.
How Does This Work?
The interesting part is water heater thermostats measure the water temperature without directly coming in contact with it. Being pressed firmly against the outer layer of the tank, it senses the temperature of the tank material to judge the water temperature.
The tank is completely insulated except for two points where the thermostats are mounted. With metal-to-metal heat transfer, it easily reads the temperature of the water.
How to Identify a Faulty Thermostat
If your water is not heating properly, it’s either the thermostat or the heating element to blame. Considering that the problem is with your thermostat, here is a quick guide on identifying which of the two needs fixing.
The two thermostats are wired so that only one of the two heating elements is turned on at a time. The first half of the job is of the upper thermostat, which ensures that the top 1/3rd part of the water in the tank has been heated up to the set temperature. After that, it switches the electricity to the lower thermostat, which is responsible for sensing the drop in temperature.
So when you notice the water heater has stopped heating, it indicates that the issue is with the upper thermostat. And since the upper thermostat controls the lower one, it won’t function unless the primary thermostat is fixed.
On the other hand, if you notice that the water is not adequately warm or runs out too quickly, the problem is with the lower thermostat. So even though the water is getting heated first by the upper thermostat, the lower thermostat is unable to sense the drop in temperature and turn on the lower heating element on time.
How to Test a Water Heater Thermostat
If you plan to check your water heater thermostats, you will also have to check on the heating elements to get a more accurate reading. The thermostats will be located under an access panel at the front of the water heater. To get started, you will need a screwdriver and a multimeter. Make sure the power is turned off before you get to work.
Shutting off the Water Heater Power
- Start by flipping the breaker switch to OFF.
- Next, to check the thermostat, remove the access cover, and insulation & protective covers.
- Connect one end of the meter to the grounded metal and the other to the two thermostats and heating elements.
- At each time, the reading on the multimeter should be zero if the power is turned off.
Checking the Thermostats for Continuity
Continuity refers to a complete path for current flow without which the heater cannot function. So once you are assured that the power is off and it’s safe to probe, follow these steps to check the thermostat:
- Check the reset button. If it tripped, reset it before moving to the next step.
- Use the screwdriver to take apart the thermostat and remove its wires. Make sure you remember how the wires are connected.
Testing the Upper Thermostat
- Connect one lead of the multimeter to the left side terminal of the reset button and the other to another terminal on the same left side.
- If the multimeter reads zero, the thermostat has continuity. Otherwise, they are faulty and need to be replaced. Repeat the same test for the two terminals on the right side.
- To test the continuity on the lower part of the thermostat, connect one lead of the multimeter to the common terminal right beside the temperature setting and the second lead to the left heating element terminal.
- Here we will need to check the resistance of the connection line. If the water temperature is below the set temperature, the resistance would be close to zero.
- Next, switch the second lead of the multimeter from the left heating element terminal to the right heating element terminal. At this point, the multimeter should read 1, or NO continuity.
- If the water temperature is above the set temperature, you will get the exact opposite results. This means that in the first case, where the multimeter is connected to the common terminal and left heating element, the reading will show 1 or No continuity.
- On the other hand, when you connect the multimeter to the right heating element and the common terminal, the reading will be zero.
Testing the Lower Thermostat
If the upper thermostat is working fine, it’s time to check the lower thermostat. The steps are pretty similar:
- Disconnect the wires and attach the multimeter to the terminals of the heating element.
- If the water temperature is lower than the set temperature, the readings will show zero ohms or resistance.
- If the water temperature exceeds the limit, the multimeter will display no continuity.
- If you get the opposite reading in these two sets, your lower thermostat is broken.
How to Replace a Faulty Water Heater Thermostat
A quick DIY guide you can use to handle the matter yourself:
- Start by shutting off the power. The first few steps would remain the same. You flip off the breaker at the main electrical panel.
- Then remove the access cover and insulation, and plastic protective covers.
- For additional safety, use the multimeter to ensure there is no current running through the appliance at the moment.
Replacing the Thermostat
- Disconnect the thermostat wires and remove them from the retaining bracket.
- Place the new thermostat in the retaining bracket (Make sure you place the upper and lower thermostats in the correct position)
- Make sure that the back of the thermostat is tightly positioned against the tank. This is an essential step to facilitate accurate temperature readings.
- Reconnect the wires as they were and put back the protective covers.
- Adjust the set temperature to 120°F on the temperature setting panel and put back the insulation and access covers.
- Turn on the water heater and run a quick trial to check if it’s heating properly.
Frequently Asked Questions
Could there be any other reasons for inadequate water heating?
Along with lower thermostat issues, another common reason for inadequate heating is sediment build-up. Over time and with constant interaction with hard water, the lower portion of the tank where the burner is located might be overloaded with sediment deposits.
This naturally disrupts the heating process and slows it down, making the water running out of the tap only mildly warm,
Do all water heaters have two thermostats?
Not necessarily. Dual thermostats are more common in bigger models with at least 20 gallons. There are plenty of smaller water heaters that come with a single thermostat. These systems are much simpler, and the fewer terminals and wirings make it easier to test and replace.
Remember, the thermostats used on these systems are not the same as the upper or lower thermostat on a dual system.
Why is my thermostat tripping?
A constantly tripping heater and thermostat is a sign of much more significant issues. It could indicate loose connections, faulty thermostats, or ground issues. A malfunctioning high-limit switch can also make the thermostat trip. It’s best to consult a professional plumber to get to the bottom of the issue as soon as possible.
How long does an average water heater last?
A water heater can last anywhere between 8 to 12 years, depending on the brand, quality, and maintenance. For longer service, get your water heater professionally serviced at least twice a year, especially after you resume using it during the winters are months of inactivity during the summer months.
Water heaters are a basic need. Whether you want to enjoy a warm shower on a cold winter morning or use lukewarm water to clean your clothes better, there is no better and more efficient way to get hot water than a functional water heater. We hope this quick guide on how to test a water heater thermostat has given you a potent fix for a faulty thermostat, allowing you to resume your hot water supply in just a few hours.
Learn How a Water Heater Works