Boiler shows E10, no operation, pressure gauge reads low or zero

Safety first: Allow the system to cool before topping up. Overfilling can cause relief valve discharge.

• Check pressure gauge: On ACV sealed systems, the gauge should typically read around 1.0–1.5 bar when cold. If below the minimum (often 0.8 bar), the boiler will lock out.
• Top up via filling loop: Locate the filling loop (flexible hose or built-in valves). Open the valves slowly until the pressure reaches the recommended cold value, then close both valves fully. Reset the boiler.
• Inspect for leaks: Walk around the property and check radiators, valves, and visible pipework for signs of water. Also inspect the discharge pipe from the pressure relief valve outside; continuous dripping indicates a fault.
• Recurrent pressure loss: If pressure drops repeatedly, the expansion vessel on the ACV boiler may have lost charge or there may be a hidden leak. A technician should test the vessel pre-charge and system for leaks.