Expansion Tank Water Heater Greater Vancouver

Many Greater Vancouver homes have backflow preventers or pressure reducing valves on the water main — and this creates a closed system where an expansion tank is required for the water heater to operate safely.

What This Means

When water is heated, it expands. In an open system, this thermal expansion pushes slightly back into the municipal supply. In a closed system (with a backflow preventer), the expanding water has nowhere to go — pressure builds in the water heater and triggers the T&P valve to relieve it. An expansion tank provides a buffer volume for this thermal expansion.

Common Causes

• Closed system indicators: pressure reducing valve (PRV) on the water main, backflow preventer, or check valve at the meter — all create a closed system
• Without expansion tank: continuous T&P valve dripping (doing its job), eventually the T&P valve wears from repeated operation and begins leaking at rest
• BC Plumbing Code: requires an expansion tank for all closed-system water heater installations

What Homeowners Can Check Safely

• If your T&P valve drips intermittently (especially during or after the water heater fires), an expansion tank issue is the likely cause

When to Call a Licensed Technician

Water heater work involves gas lines, high-voltage wiring, and pressurized plumbing. Always call a licensed gas fitter or plumber for repairs beyond basic visual checks.

• Expansion tank sizing and installation at the cold inlet to the water heater
• System pressure verification
• T&P valve replacement if the existing valve has been dripping for a prolonged period

Frequently Asked Questions

My T&P valve drips every time the water heater fires. Is that the expansion tank?

Very likely. If the T&P valve drips intermittently (especially during heating cycles) and there is a backflow preventer or PRV on the water main, the system is closed and thermal expansion is triggering the valve. An expansion tank absorbs this expansion and eliminates the dripping. Until it is corrected, the continuous valve operation will eventually wear the valve seat and the valve will begin leaking at rest.

How big should an expansion tank be for my water heater?

Expansion tank sizing depends on the water heater volume, the system pressure, and the thermal expansion at the operating temperature. A licensed plumber calculates the correct size. Using an undersized expansion tank is a common mistake — it pre-charges to the wrong pressure and provides insufficient buffer volume, allowing intermittent T&P valve operation to continue.

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