Expansion vessel in a residential natural gas boiler: operation and common faults

The expansion vessel absorbs the increase in water volume when heated and helps maintain constant circuit pressure.

How it works

Inside, there is a membrane that separates the water from the pre-charge gas.

Symptoms of failure

A large increase in pressure when the boiler heats up and a large drop when it cools down is a characteristic symptom of a problem.

Safety valve

If the pressure rises excessively, the safety valve may open and release water.

Inspection

Checking the pre-charge and resetting the vessel must be performed using the correct procedure by a technician, as it requires isolation and the correct reference pressure.