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Relief Valve Keeps Opening? Thermal Expansion Explained | Repair and Replace

Thermal Expansion in Water Heaters

 

If the relief valve in your water heater keeps on opening, then it's likely an expansion issue in the tank. In this article, we'll learn how it all works. 

The temperature and pressure relief valve is by far the most important safety device in water heaters.

 

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If the pressure or temperature inside the tank gets too high, the valve will open and release water, preventing the tank from exploding.

 

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If the relief valve opens intermittently, or even daily then it's most likely due to normal water pressure expansion.

 

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In some homes the water utility supply meter may contain a check valve, backflow preventer or water pressure reducing valve. This creates a closed system.

 

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As the water heats up, it expands. If no water is being used at the time, the water will travel back into the cold supply line.

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In a closed system this pressure has nowhere to go, so the relief valve will open to reduce the pressure.

 

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This can be fixed by installing a diaphragm-type expansion tank on the cold water supply line. In these cases it's best to contact a technician.

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On the other hand if there is a slow continuous leak then it's possible that the valve is not closing properly.

 Relief Valve Keeps Opening? Thermal Expansion Explained | Repair and Replace