Boiler display or control indicates low system pressure; boiler will not fire and pressure gauge reads below 0.5 bar.

Safety: Only top up a sealed system if you are familiar with the filling loop. Do not over-pressurise the system.

User steps to restore pressure:

• Locate the pressure gauge on or near the Grant boiler.
• Find the filling loop (usually a braided hose with two valves). Open both valves slowly and watch the gauge rise.
• Close both valves when the pressure reaches the recommended cold pressure (typically 1.0–1.5 bar; check Grant manual).
• Reset the boiler if required and check for normal operation.

If pressure keeps dropping:

• Inspect visible radiators, valves, and pipework for signs of leaks.
• Check the pressure relief valve discharge pipe outside; if dripping, the PRV or expansion vessel may be faulty.
• A qualified engineer should test and recharge or replace the expansion vessel and replace a passing pressure relief valve.

Do not repeatedly top up a system losing pressure; this introduces fresh oxygen and accelerates corrosion. Find and fix the leak.