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Plumbing Glossary

Expansion Tank

A small tank on the water heater or supply line that absorbs pressure spikes as heated water expands. Required on many closed-loop residential systems.

Expansion Tank

What it means

When water heats, it expands. On a closed system with a check valve or pressure reducer, that expansion has nowhere to go without an expansion tank. The tank's internal bladder compresses air to cushion pressure rises.

Missing or waterlogged expansion tanks cause relief valves to drip and can shorten water heater life. They are sized to match heater volume and supply pressure.

Why it matters in Santa Cruz County

Many Santa Cruz County water districts use pressure reducing stations, creating closed systems on hillside streets in Scotts Valley and the Westside. Water heater replacements in garages and interior closets should include expansion tank evaluation.

Homeowner tip

If your T and P valve drips only when the heater runs, ask about expansion tank condition before replacing the valve.

Related Wade's services

Also explore the Septic Glossary or call 831.225.4344 with questions about your property.