Thermostat displays A04 and heating is disabled

Safety first: Only operate the filling loop and user controls as described in the boiler manual. Do not open sealed boiler components.

• Check boiler pressure gauge: Go to the boiler and read the pressure gauge. For most Vokera boilers, cold pressure should be around 1.0–1.5 bar.
• Top up pressure: Locate the filling loop (usually a silver braided hose with two valves). Open the valves slowly until the pressure rises to the recommended level, then close both valves fully.
• Reset boiler: If the boiler is in lockout, press the reset button. The thermostat should clear the A04 indication once the boiler reports normal pressure.
• Inspect for leaks: Walk around the property and check visible pipework, radiators, and valves for signs of water leaks. If pressure drops again quickly, contact a heating engineer.
• If A04 persists despite correct pressure: The boiler's pressure sensor or PCB may be faulty. The thermostat is only reporting the boiler status; call a qualified engineer.