Boiler displays low water pressure fault, will not fire, pressure gauge below minimum (often below 0.5 bar)

Safety: Only top up a sealed system when it is cool. Over-pressurising a hot system can cause discharge from the safety valve.

• Check pressure gauge: Confirm the reading on the boiler's pressure gauge. If below the recommended cold pressure (usually 1.0–1.5 bar), the boiler will lock out.
• Top up via filling loop: Locate the filling loop (flexible braided hose with two valves). Open both valves slowly until the pressure gauge rises to the recommended level, then close both valves fully.
• Inspect for leaks: Walk around the property checking radiators, valves, and visible pipework for signs of water. Repair any leaks before repeated topping up.
• Reset boiler: After restoring pressure, reset the boiler using the control panel or reset button and check operation.
• Persistent pressure loss: If pressure drops repeatedly, the expansion vessel may be flat or there may be a hidden leak. A heating engineer should test the vessel pre-charge and inspect the system.