Error E23

Safety first

1) If you are not competent with appliances, call a Gas Safe engineer — do NOT open the boiler or interfere with gas/electrical components. 2) Before doing any checks, turn off external electrical loads (use the boiler’s on/off switch or the fused spur) if you will be touching pipework or valves. Do not work on the boiler internals with the mains still connected. 3) If you smell gas, evacuate the property and call the gas emergency number immediately.

Initial homeowner checks (what you can safely do)

1) Record the exact fault code and any other indicators on the display. Try pressing the boiler reset button once to see if it will clear and restart. If it restarts and remains stable, monitor pressure and operation. 2) Check the boiler water pressure gauge when the system is cold. Aim for around 1.0–1.5 bar cold. The boiler may shut down if pressure falls below ~0.2–0.4 bar depending on model settings. 3) If pressure is low, locate the filling loop (flexible hose or built-in valve under the boiler). Slowly open the filling loop valves until the gauge reads about 1.0–1.5 bar, then close the valves fully. Remove or isolate the filling loop if it is removable. 4) After topping up, press reset and see if E23 clears. 5) Check for visible leaks (under the boiler, radiators, valves, pipes, and the pressure relief discharge pipe). If pressure keeps dropping after topping up, there’s likely a leak and you should call an engineer.

If E23 remains after the above

1) Power-cycle the boiler: turn off at the fused spur, wait 30 seconds, turn back on and attempt a reset. Note any change. 2) Check whether other low-pressure related codes appear (E24, E67 or F1) which can indicate repeated pressure loss or pressure below threshold; this supports a leak or failing component. 3) If pressure is stable at the correct level but E23 persists, the pressure sensor/pressure switch or its wiring is a likely cause.

Engineer-only diagnostic and repair actions (do not attempt unless qualified)

1) Isolate mains electrical supply and gas supply and follow safe isolation procedures. 2) Remove the boiler outer case and visually inspect the water pressure switch and wiring. 3) Drain the system below the level of the appliance if the pressure switch or associated pipework must be removed (use the boiler drain/off and radiator drain points). 4) Disconnect the push-on connectors from the pressure switch, note positions, and test the switch with a multimeter while operating the filling loop to confirm it changes state at the correct pressure. 5) If the pressure switch is faulty, replace with the correct OEM part. Reassemble, refill and purge/bleed the system, restore gas and electrical supplies and test. 6) If wiring or connections to the control PCB are suspect, check continuity and connector seating; replace or repair wiring as required. 7) If the control PCB itself shows faults (repeated non-sensor related lockouts or internal errors), replacement may be necessary.

When to call a professional

1) Call a Gas Safe engineer if you are unsure at any point, if the boiler will not reset after correct pressure is restored, if pressure repeatedly drops, or if you suspect a faulty pressure switch, wiring or control PCB. 2) Any work requiring draining the system, accessing internal components, disconnecting gas or mains electricity, or replacing safety-critical parts must be done by a qualified engineer.

What to tell the engineer

Have the fault code (E23), what you’ve tried (pressure reading, whether you topped up, whether pressure falls afterwards, whether there are any visible leaks), and how often the issue occurs. This information speeds diagnosis and helps the engineer bring the right parts/tools.