Water Heaters

Thermal expansion tank: check and replace

On closed systems (check valve or PRV), heated water has nowhere to expand. An expansion tank absorbs it. Its air charge should match the static water pressure.

Single source ~45 min moderateBrands: All

Before you start

  • Scald risk; isolate and drain pressure before removing a tank

Diagnostic steps

Unlock all 4 steps with expected values

Full library + AI assistant for $34.90, one time.

Get lifetime access

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

More water heaters guides

Guide · Water Heater

Heat-pump (hybrid) water heater: slow recovery, noise, errors

Hybrids need enough room air and a clean air filter, a working condensate drain and the right mode. Many complaints are mode settings or a dirty filter. Refrigerant faults are sealed-system work.

5 steps ~60 minmoderate
Guide · Water Heater

Tankless water heater descaling (flush)

Scale insulates the heat exchanger, causing overheat codes and fluctuating temperature. Flush with a pump and descaling solution through the isolation valves.

5 steps ~75 mineasy
Guide · Water Heater

Hot water recirculation pump problems

Check timer/settings, check valves, air in the loop and the pump itself. On tankless units with built-in pumps, a recirculation code may point to air or a leak in the loop.

5 steps ~60 minmoderate
Thermal expansion tank: check and replace · OnCall Tech