Boiler shows E08 and stops; system pressure gauge is low or fluctuating.

Safety: Allow the boiler to cool before repressurising. Do not exceed the maximum system pressure stated on the CTC data plate.

• Check pressure gauge: Look at the boiler's pressure gauge. If below the recommended cold pressure (often 1.0–1.5 bar), repressurise using the filling loop.
• Repressurise system: Connect the filling loop (if detachable), open the valves slowly, and watch the gauge rise. Close the valves at the target pressure. Bleed radiators and top up again if needed.
• Inspect for leaks: Walk around the property checking radiators, valves, and visible pipework for signs of water. Repair any leaks before repeated repressurising.
• Check expansion vessel (technician): If pressure rises quickly when heating and then drops to zero when cool, the expansion vessel may be flat or waterlogged. Isolate, drain pressure, and check the vessel pre-charge with a tyre gauge. Recharge or replace the expansion vessel.
• Pressure sensor/switch (technician): If pressure is correct but E08 persists, test the water pressure sensor or switch with a multimeter. Replace the sensor if readings are incorrect.