Why Gas Water Heater Keeps Cycling ON and OFF?

It is completely normal for a gas water heater to turn on and off throughout the day. 

However, the unit might turn off too soon, in case the thermocouple is dirty, damaged, or bent, the pilot tube is dirty, the gas valve is faulty, or the air inlet is clogged. A stuck flow switch would make a tankless unit turn on more often than needed.

Do Gas Water Heaters Turn On and Off?

Usually, water heaters don’t really turn off. Even though some units might actually be working only for around 5-6 hours per day, that doesn’t mean that they are switched off the rest of the time.

When you’re not using the hot water, the appliance stays in standby mode. This fact ensures that you have heated water whenever you might need it.

You can manually turn your water heater off, in case you are going on holiday. There are also special timers that can make the unit turn on an hour before you wake up, for example.

Can a Water Heater Turn Itself Down?

The unit will run only when someone is actually using the hot water. After that, the water heater is going to turn itself down automatically – you don’t need to manually shut off the appliance.

Once the unit turns itself down, it goes into standby mode.

While some models with a tank will continue maintaining the water temperature, tankless water heaters won’t be using the power to keep the water warm. 

However, they do not completely shut down, as the units always have the components responsible for sensing the water flow running.

Read: Why Gas Hot Water Heater Is Not Heating? – Troubleshooting Guide

Why Does My Water Heater Keep Turning Off and On?

Gas and electric water heaters will keep turning on and off for different reasons.

When it comes to a gas unit, there might be something wrong with the gas supply or the thermocouple. Electric water heaters usually turn on and off if there is an electrical glitch of some sort.

Rheem Water Heater Keeps Turning Off

If you are a proud owner of a Rheem power vent water heater that keeps turning off, then the chances are high that the thermocouple is damaged, bent, or simply dirty.

In case you’re planning on inspecting and cleaning the element, don’t forget to turn the unit off and give the thermocouple enough time to cool down. 

Read: Gas Water Heater Thermocouple Possible Issues

Honeywell Water Heater Keeps Shutting Off

A faulty thermopile might make a Honeywell water heater turn off.

A thermopile is an element that generates the electricity needed to power the unit’s gas control valve. Once the pilot is lit, it will take the thermopile up to 90 seconds to get hot enough and to power the valve.

If the element is faulty, it might not sense the heat from the pilot and the thermopile with shut the unit off.

Tankless Water Heater Keeps Shutting Off

The most common things that can cause a tankless water heater to turn off include:

  • A loose wire (gas water heater have wires as well)
  • No electricity, gas, or water
  • A low water flow rate (a lot of tankless units have a minimum water flow rate requirement; if it’s not reached, then the unit will shut down)

Read: Why Water Heater Is Leaking?

Why Gas Water Heater Keeps Cycling On and Off?

A dirty thermocouple

If you are able to light the pilot, but it keeps going out, then it might be because there is something wrong with the thermocouple.

A dirty, bent, or damaged element will not sense the pilot’s flame. As a result, the thermocouple will not keep the gas supply open.

In such a case, you might have to replace the thermocouple.

A dirty pilot tube

If the pilot tube is blocked or dirty, then the pilot light might not light at all or it will be very weak.

A flickering yellow flame is the most obvious sign of a dirty pilot tube and burner.

A bad gas valve

The gas gets transferred to the unit through the gas valve. If the gas supply gets interrupted due to a malfunctioning valve, the water heater will shut down.

A clogged or dirty air inlet

Your gas water heater might have an air inlet screen right at the bottom of the unit. These screens can get clogged with dirt, hair, pet dander, and so on.

All gas burners need a constant supply of air in order to function. If the air inlet is dirty, there might not be enough airflow to keep the burners going.

Read: Is Furnace And Water Heater The Same?

Why Does My Water Heater Keep Cycling?

Tankless water heaters have temperature sensors and a flow switch. The latter activates the water heater and the sensors control the amount of heat that is delivered.

When you turn the hot-water tap, the water heater should automatically turn on. If the unit continues cycling even when you’re not using the water, then it might be because the flow switch is stuck.

Cycling in various types of water heaters can also occur when the demand load is less than the minimum firing rate of the unit

In a nutshell, the heater will continue cycling on and off, if the BTUH (British Thermal Units per Hour) required to heat the water to a set temperature is lower than the water heater’s minimum BTUH that it can operate at.

How Often Does a Gas Water Heater Cycle?

A gas water heater with a tank will cycle on and off a few times per day as it needs to keep the water in the tank hot.

Fact: the water in the tank is constantly losing a bit of heat off the walls and through the exhaust duct.

How Often Should a Gas Boiler Cycle On and Off?

A lot of boilers would naturally cycle on and off. However, if your unit is cycling more than 8-10 times per hour, then it looks like the boiler is oversized, the operating controls are set incorrectly, or the burners have been installed improperly.

Gas Water Heater Shuts Off After 5 Minutes

This might be because…

  • The thermocouple is bent, damaged, or dirty
  • The gas valve has gone bad
  • The pilot tube or burner is dirty
  • The air inlet is dirty or clogged

How Long Should a Gas Water Heater Stay On?

Water heaters don’t really fully shut down – even if the unit is not producing hot water at the moment, it is always ready to start operating.

On average, water heaters run for around 3 hours per day (this means that the unit actually produces hot water during this time and sends it to your faucets and appliances). The total operating time of a tankless water heater is generally less – about 1-2 hours.

Read: The Best Temperature For The Water Heater And Why?

What Do You Do When Your Water Heater Keeps Turning Off?

If your gas water heater is turning off, then it would be better to invite a professional to take care of the problem.

The chances are high that there is a problem with the gas supply, burner, or thermocouple, and any issues with these elements are not usually an easy DIY fix.

Why Does My Water Heater Pilot Keep Turning Off?

  1. A dirty pilot tube – the tube is the element that supplies gas to the pilot light. If the tube is partially or fully clogged, the pilot light won’t stay on.
  2. A dirty thermocouple – the thermocouple would close the gas valve if it doesn’t sense the pilot flame. A dirty element might not sense the flame at all.
  3. A bent thermocouple – the element has to be right next to the pilot light, otherwise, it will not receive the necessary heat. This is exactly what will happen if the thermocouple gets bent.
  4. A faulty thermocouple – the component might simply be faulty. In such a case, all you can do is replace the thermocouple. 
  5. Flex tube issues – this long tube connects the burner to the gas controller. If it gets clogged or damaged, gas won’t be supplied to the water heater.
  6. A faulty main control valve – this is a very rare issue, but, at one point, this element that is responsible for regulating the unit’s water and gas pressure might fail. In such a case, the gas valve will be closed.

How Do I Know If My Water Heater Thermostat Is Bad?

The signs of a faulty thermostat include:

  • No or not enough hot water
  • A constantly tripping high-limit switch
  • Slow hot water recovery
  • Water that is too hot

Out of all these issues, a tripping high-limit switch is the only thing that can make your water heater turn off.