Why your water heater is not heating, and what to do

What should you check first?

Start with the simple, safe things. Confirm the problem is the heater and not a tap, then check whether the water is cold, lukewarm or just running out too fast. Run a different hot tap to rule out a single faucet or a mixing valve.

If the whole house has no hot water, look at the power or gas first. On an electric tank, check the breaker in the panel for that circuit. On a gas tank, check that the gas valve to the heater is open and the control is set to a heating setting. Many problems end here.

If you smell gas or rotten eggs, do not touch switches or try to relight anything. Leave the house and call the gas utility's emergency line from outside. Our page on a heating emergency in winter sets out the order of steps.

Why does an electric water heater stop heating?

Four causes account for most failures.

• A tripped breaker. Reset it once. If it trips again, there is a fault, so leave it and call an electrician.
• The high-limit reset button. A safety switch behind the access panel trips on overheating. Turn the power off at the breaker before opening the panel, and have a qualified person find out why it tripped.
• A failed heating element. Many tanks have two elements. If one fails, you get lukewarm water or a small supply of hot water.
• A faulty thermostat. It may not tell the element to switch on, or it may cut off too early.

Testing elements and thermostats means working with line voltage, so this is a job for a licensed trade.

Why does a gas water heater go cold?

A gas tank needs a flame to heat. The pilot light may have blown out, or the thermocouple that proves the flame exists may have worn out and shut the gas off. Newer units have electronic ignition, which can fail or be starved of power. A blocked flue, a closed gas valve or sediment build-up on the tank bottom can also reduce output. Sediment makes a gas tank rumble and slows heating.

Relighting a pilot is something some owners do by following the label, but if it will not stay lit, stop and call a licensed gas fitter. Carbon monoxide is the hazard, so a working alarm near the heater is essential, as explained in our guide to carbon monoxide safety.

When is it time to replace the tank instead?

A tank that leaks at the base is finished, and no repair will fix it. Age tips the balance as well. A unit that is well past a decade old, has needed repeated work or is rusting at the connections is a poor repair bet. The ranges are in heating system lifespans in Canada, and the process is set out in hot water tank replacement.

Replacement is also the moment to compare options such as a heat pump water heater. A service contract can spread out repair and checkup costs, though terms differ by provider.

Quick answers