Hot Water Heater Not Working? Here’s What You Need to Know

Like any household appliance, water heaters are instruments that are prone to the effects of age and wear-and-tear. Fortunately for the DIY’er, they’re not overly-complicated instruments, and troubleshooting, diagnosing, and repairing them is often times quite easy.

First Things First: Gas v. Electric

Gas and electric water heaters both operate on the same basic principle that heat rises: Cold water enters the top of the tank, travels down a ‘dip tube’, and empties into the bottom where it’s heated by a heating mechanism. The hot water then rises to the top of the tank where it exits through the heat out pipe.

The heating mechanism in gas-powered water heaters is a simple gas burner. A thermostat inside the tank detects the temperature of the water - if it falls below a certain degree, the gas supply valve at the top of the tank will open and flow down into the burner, which is lit by either a pilot flame or an electric ignitor, depending on the type of tank.

A pilot flame is a small flame that burns continuously just below the burner. When the thermostat signals for the gas valve to open, gas flows into the burner and is ignited by the pilot flame. The pilot flame itself is regulated by a safety device called a thermocouple – if the thermocouple detects that the pilot flame has gone out, it will prevent the gas valve from opening. Oftentimes the thermocouple is the culprit in ill-functioning gas water heaters.

Hot surface ignitors are a bit more complicated, and involve a series of electrical pathways. Like pilot ignitors, they are also controlled by a thermostat, but they utilize a control board to electronically ignite the gas burner when the temperature falls below a certain level.

In this system, when the thermostat signals for the gas valve to open, the control board turns on a fan which draws fresh air into the water heater. Once the fan is up to speed, a vacuum switch turns on the electric ignitor, and then a solenoid opens the gas supply valve and the burner is ignited. A flame sensor detects whether or not the burner is lit – if it is not lit, the gas supply valve will not open.

Gas water heaters also have an exhaust flue that gets rid of carbon monoxide. A leaking or clogged flue can be a major hazard, and can cause the water heater to overheat.

As you can see, there is quite a bit that can potentially go wrong in gas-powered water heaters – especially ones with hot surface ignition. Electric heaters are simpler and more efficient.

Rather than a gas burner, two 120 volt heating elements are used to heat the tank in an electric water heater. The power supply comes from a control box on the outside of the unit. One element is suspended towards the top of the tank, and the other towards the bottom. Each is controlled by its own separate thermostat. Depending on the temperature at each element, they cycle on and off one at a time. Thermostats can be set manually on both gas and electric-powered water heaters, generally between temperatures of 120 - 160 degrees Fahrenheit.

Here are a couple excellent videos showing the main differences between gas and electric water heaters.

Troubleshooting and Diagnosing

There are essentially only a handful of situations that will indicate your water heater isn’t working properly: it will make strange, loud noises, there will be no hot water, the water will be too hot, or the hot water will not last long enough.

Now that you’ve got a basic understanding of how your water heater works, some alarm bells might be going off as to what may be causing the problem.

Water heater making loud noise:

This is almost certainly due to sediment buildup in the bottom of the tank, and can be fixed by draining the water heater. Simply open the drain valve and drain until the water comes out clear. This is actually routine maintenance, and should be done at least once a year. (Applies to both gas and electric water heaters).

No hot water:

If you have no hot water in your house at all, here are a few things to check for both a gas and an electric water heater.​

Gas Water Heater


  • Check to see if pilot light is out, or not staying lit
  • Check for defective thermocouple (*very common problem in pilot ignitor gas water heaters)
  • Check to make sure gas supply valve is working effective gas valve
  • Check for defective or clogged burner
  • Check continuity of control board for hot-surface ignition systems (fan, vacuum switch, ignitor, gas valve solenoid) *in these systems, a faulty ignitor is often the culprit

Electric Water Heater


  • Check to ensure there is power to water heater (tripped circuit breaker or blown fuse)
  • Reset button (Electric water heaters have a master thermostat; if they get too hot, the pressure relief valve will open and the reset button will be tripped. To fix, simply press reset button)
  • Check continuity of thermostat(s) and heating element(s)
  • Check for sediment accumulation and leaks

Not enough hot water:

For both gas and electric water heaters, this may be the result of a leak at one of the hot water faucets, or caused from insufficient insulation around the hot water pipes (lack of insulation will cause heat to escape).

Gas

- Check for defective or incorrectly set thermostat (you can control what temperature your thermostat is set at)

- Check for clogged burner

Electric

- Master thermostat is defective or set too low

- Check for defective heating element(s) and thermostat(s)

Water is too hot:

Gas

-Thermostat is set incorrectly, or is defective

- Exhaust flue is blocked (Checking the flue assembly is periodic maintenance that should also be done at least once a year).

Electric

- Thermostat is defective or is set incorrectly

- Insulation around thermostat is insufficient (this will cause incorrect readings and may result in tank continuously being heated)

Leaks in Water Heater:

A leaking water heater can be utterly disastrous. Turn off water supply at the shut-off valve if there is any leak at all.

Leaks can come from one of several locations:

- Hole in the tank itself (usually caused by rust/corrosion from sediment buildup or a faulty sacrificial anode)

- Drain valve

- Temperature/pressure relief valve (these are safety valves on both gas and electric water heaters. If the temperature or pressure gets too high inside the tank, the relief valve will open)

- Cold water intake/dip tube

- Heat out pipe

- Heating element seal/gasket (electric water heaters only)

Hopefully some of these symptoms ring true and you'll be well on your way to diagnosing and fixing your water heater!​

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