How to Fix / Troubleshooting

Safety: Do not repeatedly add water without finding the cause; this introduces oxygen and accelerates corrosion.

Inspect for visible leaks: Check all accessible piping, radiators, and the boiler cabinet for signs of water or rust streaks.
Check expansion tank: Tap the tank; it should sound hollow at the top and solid at the bottom. If waterlogged, it may need recharging or replacement.
Monitor relief valve: Place a container under the relief discharge pipe and monitor for intermittent dripping.
Professional pressure test: A heating contractor can pressure-test the system and isolate whether the Dettson boiler or external piping is leaking.

Boiler frequently loses pressure and needs to be topped up

Possible Causes