Signs your hot water tank may be overheating

You step into the shower and turn on the taps…yikes! The water isn’t just hot but steaming, despite your tank being set to a moderate temperature. Is this because your hot water tank is overheating? Is there a way to fix it? These tips will help ensure your hot water tank is working safely and efficiently.

Most homeowners know three things about their hot water tank: how big it is (roughly), whether it uses natural gas or electricity, and if it’s working or not. Considering that a properly working hot water heater is essential for your morning shower, doing laundry, cleaning the dishes and cooking, then it makes sense to understand a little bit more about it.

Hot water tanks are very basic in their design, but they're effective

• Traditional hot water heaters are large, insulated cylinders with a heating mechanism.
• A shut-off valve from the cold water supply pipes controls the flow of water into the heater.
• Cold water (being heavier than warm) settles to the bottom of the hot water tank.
• Natural gas water heaters have a burner at the bottom and chimney at the top.
• Electric water heaters use two heating elements inside the tank, usually positioned vertically.
• When hot, heated water rises to a heat-out pipe that flows to your hot water taps.
• All hot water tanks have a thermostat or temperature-control device.
• A drain valve near the base of the tank allow you to drain the water heater for maintenance or replacement.
• A pressure relief valve, usually at the top of the tank, keeps the pressure inside the tank at a safe level.

The most common cause for dangerously hot water coming from your tap is an improperly set thermostat. Fortunately, you can address this with a simple adjustment to the thermostat dial.

Electric water tanks
The thermostat dial is typically located behind an access panel.

• You must first disconnect the electricity before you open the panel. What’s more, if your heater has two heating elements then you may see two dials after opening the panel.

Natural gas water tanks
Certain natural-gas heated tanks have a temperature-control dial on the outside of the hot water tank.

Safe temperature ranges
You usually have the choice of setting your water temperature preference from about 49°C to 82°C with these guidelines:

• You need at least 50°C – or a medium setting – to prevent the risk of bacterial growth in the tank
• Water at 70°C and higher can cause third-degree burns within six seconds
• Water at 60°C can scald babies and young children in one second
• Water at 50°C can take five minutes to scald a child
• Injury prevention specialists recommend 50°C for households with children
• Most Canadians set their water heaters at 60°C

Natural gas
Dealing with an overheating natural gas hot water tank is the easiest because the thermostat is on the outside of the tank. If you just moved into new home, the water heater may have been set too high. Simply lower it to a safer temperature. The dial should be prominently placed at the base of the tank on front of the gas control. The marked settings include:

• Warm for 32°C to 43°C at its lower setting
• Warm for 50°C at its middle setting
• Hot for an average of 60°C to 65°C
• Low for a vacation setting when the tank is not in use

Electric
On an electric hot water tank, the thermostat is hidden behind an access panel, but you can adjust the temperature with a work light, a flat blade screwdriver and a few simple steps:

1. Turn off the water heater breaker to cut off all power to the tank
2. For a double element model remove both access panels
3. A single element model has only one panel
4. Pull back the insulation that behind the panel(s)
5. Find the thermostat just above the heating element
6. Locate the thermostat adjusting screw and the marked temperatures
7. Using the flat blade screwdriver, set the thermostat to the desired temperature
8. Put back the insulation and panels; reset the breaker

What if you have your hot water tank set at the right temperature for safety and your needs, but the water still feels too hot?  Measure the difference between your water heater setting and the temperature of the water coming out of your faucet. To do this:

1. Use a meat or candy thermometer, not a fever thermometer
2. Run water from the hot water tap into a glass
3. Put the thermometer in the glass
4. Keep running the hot water into the glass for at least a minute
5. Read the thermometer until the temperature stops rising
6. You have your real water temperature

If the reading you observed is significantly higher – more than a few allowable degrees – your hot water tank is most likely overheating. Why? Here are some reasons to consider before you call a plumber:

• A poorly adjusted thermostat inside an electric water heater
• Deposits from hard water inside the tank and on the heating elements
• Old, failing heating elements
• A faulty thermostat or temperature controller on an electric water heater
• A failing thermostat because of a faulty gas valve on a gas water heater

In the case of a faulty or malfunctioning thermostat, the heat in your hot water tank is on all the time, rather than cycling on and off to maintain a constant temperature. This causes pressure to build in the tank as well.

If you are handy and regularly drain your hot water tank to clean out sediment and deposits, you can avoid some problems. Basic maintenance can help make your water heater last.

However, don’t hesitate to call a professional for the serious problem of an overheating hot water tank. A licensed plumber can give you a total inspection and diagnosis, including:

• Checking the pressure release valve
• Assessing the condition of the heating element or gas valve
• Testing the thermostat
• Checking for corrosion and mineral deposits

When all is said and done, take the advice of a trusted and reliable plumber since some repairs can be expensive, especially for a very old or natural gas hot water tank. Have your plumber provide a detailed repair estimate and ask questions. Any reputable plumber will help you realistically weigh the benefits of repairing versus replacing a hot water tank that is overheating.

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Got a question we haven’t answered? Check out our Plumbing Tips & Advice section for even more practical advice, handy hints, helpful pointers and expert tips.