Boiler pressure advice
Low boiler pressure?
Use the right instructions for your boiler.
A sealed heating system needs enough pressure to circulate water. If the gauge or display shows low pressure, the boiler may stop—but filling arrangements and normal readings differ between models.
Start with the manual
Find the boiler make and model and follow its own instructions. Some systems use an external filling loop, while others have a built-in key, lever or different filling arrangement.
Check the pressure when the system is cool. The correct normal range is the one stated by the manufacturer, not a universal number taken from another boiler.
The general process
- Turn the heating off and let it coolThis gives a more useful pressure reading and reduces the risk from hot components or water.
- Identify the correct filling controlsUse the diagram in the boiler manual. Do not operate a valve simply because it is nearby.
- Add water slowlyOpen the specified control gently while watching the gauge or display.
- Stop at the stated pressureClose every filling control fully as soon as the manufacturer’s recommended cold pressure is reached.
- Restart as instructedUse the manual’s procedure, then check that the filling controls are closed and there are no visible leaks.
When topping up is not a lasting fix
Pressure can change after radiators are bled, but repeated pressure loss, a gauge that rises sharply when hot, or water appearing from pipework needs investigation.
Do not keep adding water to a system that repeatedly loses pressure. Note how quickly it falls and tell the engineer about any visible drips, recently bled radiators or fault codes.
