Thermal Expansion

Water expands when it is heated. In an older, open plumbing system that expansion simply pushed back toward the city main — but modern systems with a check valve, backflow preventer or pressure-reducing valve are closed, and that extra volume has nowhere to go.

The result is a pressure spike every time the water heater fires. Over time those spikes show up as dripping relief valves, leaking faucets and supply connections, running toilets, noisy pipes, and a water heater that fails years early. It is one of the most misdiagnosed conditions in residential plumbing.

The fix is a properly sized and correctly charged thermal expansion tank on the cold water supply, often alongside a pressure-reducing valve. Sizing depends on your water heater capacity and your incoming static pressure, and the tank's pre-charge has to match that pressure — a tank installed without that check does very little.

B&L Plumbing tests your system pressure, confirms whether your system is closed, and installs expansion control that meets code. If you're replacing a water heater, this is the moment to get it right.