Error E20

Safety precautions:

- If you smell gas, evacuate the property immediately and call the gas emergency number. Do not attempt any checks.

- Before doing any work on the boiler, switch off electrical power at the isolator and, if possible, switch off the room thermostat or controls to prevent the boiler from trying to run while you are checking it.

- Do not open gas valves, remove gas fittings or work on live wiring unless you are a qualified engineer. If in doubt, call a Gas Safe registered engineer.

Initial checks a homeowner can do:

1. Reset the boiler: switch off at the mains isolator, wait 30 seconds, then switch back on and try to restart. Some sensor errors clear after a reset if they were intermittent.

2. Check system pressure: look at the pressure gauge. If pressure is low (under about 1.0 bar) repressurise to the normal working pressure (typically around 1.2 to 1.5 bar) using the filling loop. If you are not confident doing this, call a heating engineer.

3. Check room thermostat and timers: confirm the heating demand is set correctly and batteries in wireless controls are OK. A faulty controller can sometimes appear as a sensor problem to the boiler.

4. Look for visible signs: inspect around the boiler for condensation, corrosion, water leaks or damaged wiring to external probes. Do not remove the boiler cover or touch internal parts if you are not competent.

Specific diagnostic and fix steps (what an engineer will do):

1. Read full fault history from the boiler service menu to see if this is intermittent or persistent.

2. If safe, the engineer will check the wiring and connector for the central heating NTC sensor for loose connections, corrosion, chafing or signs of water ingress. Re-seating or replacing a corroded connector often fixes the issue.

3. The engineer will measure the thermistor resistance at room temperature with a multimeter and compare it to the manufacturer specification. An NTC sensor that reads open circuit or out-of-spec indicates the sensor needs replacement.

4. If the sensor and wiring test good, the engineer will check continuity from the sensor connector back to the PCB and test for any short to earth or intermittent breaks.

5. If wiring and sensor are good but the boiler still reports E20, the engineer will evaluate the PCB and related electronics. Faulty inputs or PCB faults sometimes mimic a sensor failure and may require repair or replacement by a qualified technician.

6. After repair or replacement, the engineer will clear the fault code, run the boiler through a full operational check, and confirm flow and return temperatures, proper ignition and safe operation.

When to call a professional:

- If reset and simple checks do not clear the code, call a qualified Gas Safe registered heating engineer. Any internal electrical work, sensor replacement, PCB work or gas-side checks must be done by a professional.

- If the boiler repeatedly shows E20, loses heating, or other fault codes appear, book a service to avoid repeated lockouts and potential further damage.

Additional notes:

- Avoid attempting internal repairs or swapping electronic components yourself; incorrect work can create safety risks and will likely invalidate any warranty or service agreements.

- If you must leave the boiler off for safety, turn off the electrical supply and isolate the boiler until the engineer arrives. Provide the engineer with the exact model and the error code and any recent events (power cuts, freezes, water leaks) that may help diagnosis.