Boiler Expansion Tank Troubleshooting

Updated February 21, 2017

A boiler expansion tank refers to a small tank used in boiler systems to absorb excess water pressure. Boiler expansion tanks can experience problems for numerous reasons, which can usually be resolved via basic troubleshooting.

Leaking Relief Valve

Air in the expansion tank may be absorbed into the heated water, resulting in an overloaded, or waterlogged, expansion tank. This often leads to leakage in the relief valve, the valve which opens to relieve pressure in a system. The operator should drain the expansion tank via the drain valve and replace the relief valve if damaged.

Clogged Relief Valve

If the relief valve leaks for any reason, minerals from the escaping water can accumulate in the valve. This stops the valve's leakage, but the pressure build-up can cause the tank to explode. The operator should drain the tank using the drain valve and thoroughly clean the relief valve of any sediment.

Ruptured Diaphragm

Older style boiler expansion tanks contain a diaphragm, a bladder composed of elastic material that expands to hold water and contracts to release it. A ruptured diaphragm can cause water to spill into the upper half of the expansion tank, resulting in impaired expansion tank operation. Replacing the diaphragm typically restores boiler expansion tank function.

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