How to Fix / Troubleshooting

Safety first: Allow the system to cool before inspecting for leaks.

Inspect for visible leaks: Check all radiators, valves, and visible pipework for dampness or staining.
Check safety valve discharge: Look at the safety valve outlet pipe outside; if it drips when the boiler heats, the valve may be passing or the expansion vessel failed.
Test expansion vessel: With the system depressurised, measure the air charge at the vessel Schrader valve. Recharge or replace if flat or waterlogged.
Monitor pressure: After topping up, note how quickly pressure drops to help locate the issue.

When to call a professional: Expansion vessel replacement or hidden leak detection should be done by a heating engineer.

Boiler frequently loses pressure and needs regular topping up.

Possible Causes