Boiler display shows E04 and shuts down. Often associated with low or no water in the system. Radiators are cold and pressure gauge is near zero.

Safety first: Allow the boiler to cool before adding water. Do not over-pressurise the system. Typical cold pressure is 1.0–1.5 bar unless Viadrus documentation specifies otherwise.

Step-by-step checks:

• 1. Read the pressure gauge: Locate the system pressure gauge on the boiler fascia or underneath. If below 0.8 bar, the boiler may lock out with E04.
• 2. Top up the system: Find the filling loop (flexible hose with two valves) connected to the Viadrus boiler. Open one valve fully, then slowly open the second while watching the gauge. Close both valves when the pressure reaches about 1.2 bar. Remove the hose if the manufacturer requires.
• 3. Bleed radiators: Starting from the lowest floor, bleed each radiator using a bleed key until water appears. Re-check pressure and top up again if needed.
• 4. Inspect for leaks: Walk around the property and check all radiators, valves, and visible pipework for damp patches or drips. Inspect the boiler underside for signs of water. Persistent pressure loss indicates a leak or faulty expansion vessel.
• 5. Check pressure sensor/switch: If the gauge shows correct pressure but E04 remains, the water pressure sensor or switch may be faulty. Inspect its wiring and connector. Replacement usually requires draining the boiler and should be done by a technician.

When to stop: If you must top up frequently (more than once every few months), or if E04 persists with correct pressure, contact a heating engineer to check for leaks, expansion vessel failure, or a defective pressure sensor.