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Water Heater Not Heating? Here’s Why (+ How To Fix)

A water heater is a must-have home appliance in every home. From the hot water at your kitchen sink to the laundry and an adequate hot water supply for showers, having a functional water heater is no doubt invaluable. However, a water heater could fail and stop heating, and you need to know what the problem is and how to fix it.

If your water heater isn’t heating, one of these 7 problems could be the cause:

  • Problems with the energy supply.
  • The top heating element has failed.
  • A faulty upper heating element thermostat.
  • A tripped high-limit switch.
  • A damaged water heater dip tube.
  • A  blown-out pilot light.
  • A bad thermocouple.

We’ll discuss these problems and their solutions in the rest of the article. Since water heaters are usually electric or gas-powered, some issues and fixes will be specific to gas or electric heaters. We’ll also call your attention to water heater issues that require the expertise of a professional along the way.

Problems With the Energy Supply

The first thing you should suspect if your water heater isn’t heating is an energy issue. This could mean no electricity flow for electric heaters, or both electricity and gas have problems in gas heaters.

Power issues that can cause your water heater not to heat include:

  • The water heater switch is not turned on.
  • A tripped circuit breaker or a fuse that’s blown.
  • No gas supply.

How To Fix Water Heater Power Issues

Depending on the power issue affecting your water heater, perform the following fixes:

  1. First, check to ensure that the water heater is turned on and the power indicator is lit.
  2. If the issue is not with the power switch, check if the circuit breaker supplying the water heater is tripped, or the fuse burned.

Reset a tripped circuit breaker by flipping the switch to the on position (upwards). If the switch feels hard to flip, don’t force it. Call a trained electrician instead to service the circuit breaker.

  1. If you have a fuse box in place of a circuit breaker, check to see if the fuse has a broken filament, or the fuse tube has a dirty residue. If so, the fuse is burned and should be replaced.

If you have a gas water heater, perform one of the following fixes:

  • Hold the pilot knob down for a while to purge out any air in the gas line that’s blocking the gas flow.
  • Check if the gas valve is turned off (it sits at an angle to the gas supply pipe). If so, turn the gas supply valve to the on position (parallel to the pipe).
  • Run another appliance in the home that uses gas to see if it works. If it doesn’t, your gas line may not be delivering gas to your home. Call the municipal supplier.

If power or gas supply isn’t the cause of your water heater not heating, proceed to check for other possible causes.

The Top Heating Element Has Failed

Electric water heaters have a top and bottom heating element. The top heating regulates the thermostat for both heating elements. If the top element fails, the thermostat will not trigger the bottom heating element. As a result, the heater will not heat even though it has a sound bottom heating element.

There are several reasons a water heater heating element will fail:

  • A power surge overloads the heating element and causes it to burn out.
  • There is water sediment buildup due to water minerals like calcium and magnesium. These minerals collect at the bottom of the tank and limit the heat transfer to the water, causing the heating element to work harder than required and burn out.
  • A ‘dry fire occurrence’ if the installer forgets to open the hot water tap while the water tank is filling with cold water for the first time. This creates an air pocket which causes heat to melt the copper of the heating element.
  • A cracked water heater due to sediment buildup, damaged components, or rust. This disrupts electricity flow in the coil. A cracked water heater has to be replaced.

To prevent water heater element failure:

  • Protect your water heater heating element by installing a power surge protector, turning off power to the heater during storms, having the heater’s wiring inspected regularly, and promptly fixing any faulty wires.
  • Drain your water heater tank regularly to prevent sediment buildup.
  • Ensure the hot water tap is open when the heater’s tank is filled during installation.

How To Replace a Water Heater Heating Element

Replacing a water heater element is a long but relatively straightforward DIY task. Follow these steps to replace a failed water heater element:

  1. Turn off power to the water heater by flipping the two circuit breakers that supply the heater to the ‘OFF’ position.
  2. Wear gloves to shield your hands.
  3. Turn off the cold-water supply line.
  4. Find the water heater tank drain valve and attach a hose to drain the water.
  5. Leave a hot water tap open at one of the outlets in the home, or turn the relief valve to the open position to get rid of the pressure.
  6. Drain the water heater tank by opening the drain valve. Ensure you’ve run the hose outside before opening the drain valve. When changing the top heating element, it is enough to drain the tank halfway.
  7. Unscrew the heating element access cover to remove it.
  8. Lift the insulation to reveal the heating element. Hold the insulation onto the tank with sellotape.
  9. Remove the plastic shield.
  10. Loosen the two screws securing the heating element wires and disconnect.
  11. Confirm that your heating element is bad by testing it with a multimeter. The multimeter should be at the lowest ohms setting. A reading between 10-16 shows a sound element. No reading means a bad element.
  12. Remove the screws holding the heating element to the tank and pull the element out.
  13. Push in the new element and fasten the screws.
  14. Reconnect the element wires and tighten the securing screws.
  15. Place back the plastic shield and fit the insulation back in its place.
  16. Screw back the element cover.
  17. Move the valve to the closed position and remove the drain hose. If you had opened the relief valve, close it too.
  18. Turn on the cold water to fill the water heater tank. Turn off the hot water tap when water begins to run.
  19. Ensure the tank is filled up before turning on the heater at the circuit breaker.

This YouTube video by Sears PartsDirect is a visual aid for these steps:

If you don’t feel up to the task, hire the services of a trained plumber to replace the heating element.

A Faulty Upper Heating Element Thermostat

Electric water heaters have a thermostat attached to each of the heating elements. When power is turned on to heat the water, the thermostat at the upper heating element continuously sends current to the upper element. This happens until the water on the upper third of the upper tank reaches the set temperature.

Once the water in the upper part of the water is heated, the upper thermostat is turned off. The upper heating element then transfers power to the lower heating element to heat the water at the lower tank. The lower element also cycles on and off to maintain the water temperature once all the water in the tank is heated to the set temperature.

If the thermostat at the upper heating element is faulty, the water heater will not heat even if the thermostat at the lower heating element is sound. If the thermostat at the lower heating element is faulty, the water will still be heated to the warmth provided by the upper heating element.

You need to test and replace a faulty upper element thermostat.

How To Test and Replace an Upper Element Thermostat

Before replacing a water heater thermostat, test it for continuity to ensure it is the culprit for a water heater not heating.

Follow these steps to test the water heater upper thermostat for continuity:

  1. Turn off the water heater’s power switch.
  2. Remove the heating element access panel.
  3. Release the connection wires while noting where each goes. Removing the wires isolates the thermostat from the electrical current.
  4. Move the multimeter to the lowest ohms setting and touch one left-side terminal of the reset part (upper part) of the thermostat with one multimeter probe and the other left-side terminal with the other probe. The multimeter will display a reading close to zero if the thermostat has continuity. If it does not change, the thermostat should be replaced.
  5. Repeat the test with the right-side terminals.
  6. Test the lower part of the thermostat by placing one multimeter probe on the common terminal and the other on the upper element terminal (left side terminal). The reading should show close to zero ohms if the water is below the set temperature.

Repeat the test with the lower heating element terminal (right side terminal). The reading should show no resistance if the water is below the set temperature and a close to zero reading if the water is at the set temperature.

You can follow these steps in this YouTube video from Repair Clinic:

If you’ve determined that the thermostat is faulty, proceed to replace it using the steps below. We assume you already have the heating element exposed and the connection wires removed from the testing stage explained above. So, we’ll go straight to removing the thermostat.

  1. To remove the thermostat, locate the tabs at the top of the thermostat bracket and pull them towards you, then push the thermostat up to take it out.
  2. Fit the new thermostat in the bracket and ensure it sits securely behind the tabs.
  3. Reattach the connection wires and fasten the screws.
  4. Replace the plastic shield and the insulation.
  5. Place the access cover and screw it in place.
  6. Turn on the heater at the circuit breaker and wait to see if it resumes heating.

This YouTube video from Sears PartsDirect shows the complete process of replacing a faulty water heater thermostat:

A Tripped High-Limit Switch

The high-limit switch, also known as the high-temperature cutoff switch or water heater reset button, is situated at the top part of the upper heating element thermostat. The function of the high-limit switch is to stop the water heater temperature from exceeding the set temperature. As such, the limit switch will trip should the temperature in the water heater tank go above the set limit.

There are several reasons that can cause the high-limit switch to trip:

  • A faulty thermostat.
  • A defective heating element.
  • Loose water heater wiring.
  • Extreme water-sediment buildup.

A tripped high-limit switch stops the heating process, which is why you’ll complain your water heater isn’t heating.

How To Fix a Tripped Water Heater High-Limit Switch

Fixing a tripped water heater high-limit switch is easy if no other component failure issues are linked to it. You simply need to reset the button following these steps:

  1. Turn off power to the heater.
  2. Remove the screws holding the upper heating element access panel.
  3. Lift the insulation. You’ll be able to see the red water heater reset button.
  4. Push the reset button back in.
  5. Put back the insulation and replace the access panel.
  6. Power the water heater. It should resume heating water normally.

If the water heater high-limit switch trips again after resetting, trace the triggering issue among those listed above. Alternatively, call a trained water heater technician if you’re not sure how to proceed, especially if you suspect issues with the water heater wiring.

A Damaged Water Heater Dip Tube

The dip tube in a water heater is a plastic tube attached to the cold-water inlet at the top of the water heater. The dip tube refills the water tank as hot water is used up.

The mechanism works in a way that the incoming cold water does not mix with the hot water. Instead, the cold water is sent to the bottom of the tank for heating before being pushed up the tank and out through the hot water outlet.

A damaged dip tube is rare with modern water heaters. However, it’s possible, especially if you have an old water heater. The dip tube may tear with wear and leak cold water to the top of the tank, cooling the already heated water. This is why you’ll get the impression that your water heater is not heating.

If you have an old water heater, talk to a water heater expert to know if it’s time to replace the entire appliance. According to Energy.gov, water heaters have an estimated life expectancy of 13 years. If your water heater is new and in good condition, replace a damaged dip tube.

How To Replace a Damaged Water Heater Dip Tube

You can tell if the dip tube in your water tank is damaged if:

  • The water from your hot water tap starts out hot but gets cold soon after.
  • You notice pieces of plastic coming out of the hot water tap.
  • Pockets of hot and cold water come out of the hot water tap in turns.

To replace a damaged water heater dip tube, follow these steps:

  1. Turn off electricity to the water heater and gas for gas water heaters.
  2. Shut the cold-water supply line at the water heater shut off or the main home water supply shut off.
  3. Open the hot water tap to let out the pressure in the tank.
  4. Attach a hose to the water heater drain valve and allow 5-10 gallons (22.7-45.5 liters) of water to run out. This will help you work better.
  5. Loosen the tubing of the cold-water supply to disconnect from the dip tube. The two are usually connected with a flex connector.
  6. Remove the gasket and spin the old dip tube anticlockwise with a pipe wrench or pliers to remove it.
  7. Measure the length of the old tube and use it to size the new tube. Should the old tube be too damaged to use as a gauge, consider that dip tubes are around 3-4 inches (7.6-10.2 cm) above the control valve.
  8. Put Teflon tape on the lower side of the dip tube threader.
  9. Dip the tube into the tank and turn it clockwise to tighten.
  10. Use a flex connector or a ball valve & female pecs (depending on the type of piping you have) to finish the connection point.
  11. Replace the gasket and screw on the cold-water inlet pipe to the new dip tube.
  12. Reopen the cold-water supply.
  13. Turn on the water heater (power or power & gas) once the tank is full and check to see if the water heats as it should.

This YouTube video from Pros DIY gives you more detail on replacing a damaged water heater dip tube:

A Blown-Out Pilot Light

A gas water heater has a pilot light, a tiny flame that stays on always to light the burner when the signal is sent from the thermostat.

If the pilot light goes off due to gas or airflow issues or is faulty, the water heater will not turn on. You need to relight the pilot light or replace the pilot assembly as the case requires.

How To Relight a Water Heater Pilot Light/Replace Pilot Assembly

If the pilot light has gone off due to gas or airflow issues, it’s enough to relight it to get your water heating again. To do so:

  1. Ensure the gas is turned on at the gas control. The valve should be parallel to the gas pipe in this case.
  2. Turn the gas and thermostat controls to the pilot position. You should see ‘Pilot’ on the control knob.
  3. Hold the control down and press the spark igniter until the pilot light appears.
  4. Hold on for 3 minutes, so the igniter warms up and stays on.
  5. With the pilot on, turn the gas control from the ‘pilot’ to the ‘on’ position.
  6. Dial the thermostat knob to the desired temperature. The main burner should fire up and heat the water.

If you don’t succeed in turning back the pilot light after several attempts, the component is faulty and needs replacement. We recommend calling a trained water heater technician, as this process is complex.

If, instead, you have training in water heater appliances or are sure you can safely complete the replacement process, follow these steps:

  1. Turn off the gas supply at the gas control valve. The valve should be at a 90-angle to the gas pipe.
  2. Remove the cover of the outer burner assembly.
  3. Disconnect the spark and thermostat wires.
  4. Loosen the compression nut and disconnect the pilot gas tube from the gas valve.
  5. Release the thermocouple by unthreading the nut that holds it to the valve.
  6. Disconnect the main burner tube from the valve by unthreading the securing nut.
  7. Release the burner tube assembly by loosening the two mounting screws and pulling the assembly out.
  8. With the assembly out, turn it upside down and unthread the two screws holding the main burner head.
  9. Turn the assembly back up and use a screwdriver to release the clips holding the insulator block. Mark the position of the tube and the wires.
  10. Remove the screws holding the pilot assembly and pull the assembly out.
  11. Use the old assembly to reproduce the contour of the old tube on the new tube.
  12. Remove the fitting from the old tube by unthreading the nut and fitting it onto the new tube. Then thread the nut onto the new tube. Check to see if the pilot light orifice is in place.
  13. Move the thermocouple from the old assembly to the new one. You can also opt for a new thermocouple if the old one has served for a long time.
  14. Take the spark igniter wire insulator from the old assembly and slide it into the new assembly. You can also buy a new insulator.
  15. Reinstall the new pilot assembly by first pushing the wires and tube through the plate, then aligning it at the bracket. Replace the screws you took out earlier to secure.
  16. Follow the reverse steps to replace everything else: the insulator block, the burner head, the burner assembly, the burner tube, the thermocouple, the pilot gas tube, the spark and thermostat wires, and the outer burner assembly cover.
  17. Turn on the gas assembly valve and run the heater to see if it starts heating the water.

You can simplify this process by following this YouTube video from Repair Clinic:

A Bad Thermocouple

A thermocouple is a component on the pilot burner assembly that senses when the water heater pilot light is on. It then generates an electrical current to send signals to the gas valve to open.

If the thermocouple is bad, it will not signal the gas valve to open, and the pilot light will go off. As a result, the water heater burners will not turn on, and the water will not be heated.

A bad thermocouple needs to be replaced.

How To Replace a Bad Water Heater Thermocouple

Before replacing a water heater thermocouple, test it to confirm that it’s faulty using these steps:

  1. Remove the burner assembly outer cover.
  2. Set the multimeter to the DC range.
  3. Remove the thermocouple by unscrewing it from the control valve.
  4. Touch the copper part of the thermocouple with one of the multimeter probes and the end of the thermocouple with the other probe.
  5. With the pilot control set to the ‘pilot’ position, push the button down and press the spark igniter until the pilot lights.
  6. The voltage on the multimeter should start rising as the thermocouple heats up. If the thermocouple is good, the multimeter display will show around 20-30 millivolts. If the reading is below 20 millivolts, the thermocouple is bad and needs replacement.

Proceed with the steps below to replace a bad thermocouple:

  1. Shut off the gas supply to the water heater so that the handle sits perpendicular to the gas pipe.
  2. Allow the burner to cool from the testing steps above.
  3. Turn the control valve to the ‘off’ position.
  4. Detach the ignitor wire.
  5. Disconnect the wires from the thermal switch.
  6. Unscrew and remove the thermocouple, pilot tube, and manifold tube.
  7. Unscrew the pilot assembly and pull it out.
  8. With the assembly out, detach the wires from the plug that holds them.
  9. Pass the wires and pilot tube through the manifold door.
  10. Detach the thermocouple wire from the assembly or slide it out if the model uses a push fitting type.
  11. Place the new thermocouple where the old one was and fasten the thermocouple wire into the assembly plug. Pass the tubes back through the manifold door.
  12. Fix the plug and fasten the screws of the pilot assembly.
  13. Push the burner assembly back into the tank.
  14. Follow the reverse steps to fix the thermocouple, pilot tube, and manifold tube. Then reattach the thermal switch and ignitor wires and screw back the burner assembly outer cover.
  15. Turn on the gas supply.
  16. Turn the gas control valve to the ‘pilot’ position and light the pilot light, then turn the valve to the ‘on’ position. Your water heater should stay on and start heating the water.

You can watch these steps on this YouTube video from Repair & Replace:

Other water heater problems that could cause it to stop heating include:

  • A malfunctioning water control valve.
  • A faulty pressure switch.
  • A water heater that’s too old.

Remember that testing and replacing water heater parts can be risky if you’re not sure of the steps. Always opt to call a trained water heater expert when in doubt. As the saying goes, “it’s “better safe than sorry” for both you and your costly water heating appliance.

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Author

  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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