Error EC 256

Safety precautions:

If you smell gas, leave the property immediately, do not operate electrical switches or the boiler, and call the gas emergency number. Always isolate the boiler power at the mains before opening any cover or attempting internal inspections. Do not attempt to repair or replace internal control boards, ignition components, gas valves, or wiring unless you are a qualified Gas Safe engineer.

Initial homeowner checks (safe, non-intrusive):

1. Note and record the full display exactly as shown (EC 256 and any flashing cause code or secondary code). Also note when the fault started and any recent work or power outages. This information is useful for the engineer.

2. Try a simple reset following the GB162 manual: either press and hold the reset button for 3 seconds or turn the temperature dial to the reset position and hold for 3 seconds (then return dial to normal). Wait to see if the boiler re-lights and the code clears.

3. If the reset does not work, switch the boiler off at the isolation switch or at the fused spur, leave off for 30 seconds, then switch back on and try another reset. If the code returns immediately or repeatedly, stop attempting resets.

4. Check the mains power supply to the boiler (fuse, RCD) and ensure the house hasn’t had a recent brown/blackout; brief power surges can cause control errors. Check the display for any additional cause codes by pressing the spanner/return or info button (per your manual) and note any three-digit cause code.

5. Visually inspect (from outside) the flue outlet for obvious blockages (birds’ nests, debris). Do not insert anything into the flue. If you find a blockage, do not run the boiler and call an engineer.

Specific diagnostic and fix steps (for a qualified engineer):

1. Engineer will interrogate the boiler fault log and cause code (use spanner/return to read). They will check for related errors (e.g., F0, F7, EA codes) that indicate upstream issues.

2. Check and test all low-voltage connectors and plug-in modules (HCM/KIM/code plug and burner control unit connections) for secure seating, corrosion or damage. Re-seat connectors and retest.

3. Verify software/firmware compatibility between the burner control unit and the KIM/code plug if present; replace incorrect or incompatible modules if required.

4. Run component tests (fan, pump, ignition sequence) from service mode to see if a peripheral failure is causing the control error. Test ignition transformer, electrodes, gas valve operation and flame detection circuitry if called for by diagnostics.

5. Inspect PCB for visible damage (burn marks, blown components, bulging capacitors) and test board voltages where appropriate. Replace burner control unit / HCM board if internal board faults are found or if diagnostics indicate control unit failure.

6. After repairs or component replacements, clear fault codes and perform multiple start-up cycles to confirm stable operation. Re-check for any other underlying faults that may have contributed to the control-unit error.

Important notes and when to call a professional:

Do not attempt internal electrical or gas-related repairs yourself. EC 256 normally requires a Gas Safe registered engineer to diagnose and replace the burner control unit or related modules. If the error persists after simple resets or if additional cause codes are present, contact a qualified engineer and provide them with the recorded fault codes and circumstances. Repeated resetting is not recommended; it can mask a persistent fault and could leave the boiler operating unsafely if it does re-start. If you are unsure or uncomfortable at any stage, arrange for a Gas Safe engineer to attend.