Error E128

Safety precautions:

1) If you smell gas: leave the building immediately, avoid using phones or switches inside, call the gas emergency number and a Gas-Safe engineer from a safe location.

2) If you suspect carbon monoxide (headaches, nausea, yellow/orange instead of blue flame on other appliances, or soot): turn the boiler off at the isolator, ventilate, leave the property if symptoms are severe and call Gas-Safe immediately. Do not attempt internal repairs.

3) Always isolate electrical power to the boiler before attempting any visual inspection inside covers. If in doubt, leave it to a professional.

4) Do not open or tamper with gas valves, injectors, ignition leads, flame sensors, or the fan — these are gas/combustion components requiring a Gas-Safe engineer.

Initial homeowner checks (safe, quick checks you can do):

1) Note the fault: write down E128 and any other displayed codes and when they occurred. Do not keep repeatedly resetting more than once.

2) Try a single controlled reset: follow the boiler manual reset procedure (usually press and hold the reset button for 3–5 seconds). If it restarts and runs normally for a while, still arrange an engineer inspection — intermittent faults often return.

3) Check other gas appliances: light a gas hob or cooker to confirm there is a gas supply. If they won’t light, the issue may be a gas supply problem — contact your gas supplier.

4) Check mains power and boiler display: if display dim or other electrical faults are present, there may be a low-voltage issue. Check the fuse/trip and that the boiler’s electrical isolation switch is on.

5) Check condensate pipe (in freezing weather): if condensate is frozen the boiler can fail to operate. If you find a frozen condensate pipe, safely thaw with lukewarm water or towels; do not pour boiling water down the pipe. After thawing, reset the boiler.

6) Visual check of flue/external vents: ensure the external flue outlet and air inlets are not blocked by debris, bird nests, leaves, snow or ice. Clear any safe, external obstructions and then reset.

7) Check system water pressure on the boiler gauge — although E128 is a flame fault, very low pressure or circulation issues can indirectly affect operation. Re-pressurise only if you know how via the filling loop and within the manual guidelines.

Specific diagnostic and fix steps (for a qualified engineer / to understand what will be checked):

1) Check fault history and run the boiler through diagnostic mode to confirm flame failure count, timing and conditions (startup vs steady flame).

2) Verify gas supply at meter and inlet pressure to the appliance. Check for any recent changes to the gas service or supplier work. Measure gas pressure at the test point while calling for combustion if appropriate.

3) Inspect wiring and earth connections to the gas valve, ignition transformer, flame probe (ionisation electrode) and PCB for loose connections, corrosion or damaged insulation.

4) Test flame detection circuit: measure the flame signal (microamps) when burner lights. A weak or absent flame signal points to a fouled/damaged flame probe or wiring/PCB problem.

5) Inspect and, if necessary, clean or replace the ignition electrode/lead and flame probe. Replace if corroded or the signal does not meet specification.

6) Check the gas valve operation and supply to the valve. Measure valve coil voltages during ignition sequence. Replace gas valve if it is sticking or not operating correctly.

7) Check the fan and pressure/air proving switches and flue thermostat: ensure the fan runs and that the flue/air proving sensors are functioning and not causing premature shutdown.

8) Inspect flue for blockage or condensation issues and check flue thermostat and overheat sensors. Replace faulty flue or sensors as needed.

9) Check PCB/ignition module operation and earth reference. If all peripheral checks are good but ignition/flame detection remains unreliable, the PCB or ignition module may be faulty and require replacement.

10) Perform combustion analysis and safety checks after repair: correct gas pressure, correct gas/air ratio, CO/CO2 within safe limits, and ensure safe shutdown behavior. Run the boiler through several start/stop cycles to confirm the issue is resolved.

When to call a professional and final notes:

1) Because E128 relates to ignition and flame safety, do not attempt internal repairs yourself. Call a Gas-Safe registered engineer to diagnose and fix the fault.

2) If the fault returns after a reset, or if you have repeated lockouts, schedule an engineer promptly rather than repeatedly resetting the boiler.

3) If you smell gas or see signs of combustion problems or CO, evacuate and call emergency services/Gas-Safe immediately.

4) When contacting an engineer, give them the exact model, the E128 code, how many lockouts have happened, any other codes and what initial checks you have already done — this speeds diagnosis.

Remember: E128 is a protective lockout for flame loss. It can be caused by simple external issues (frozen condensate, blocked flue, no gas supply) but can also indicate component failure (igniter, probe, gas valve, PCB). Safety-first: leave gas- and combustion-related repairs to a qualified Gas-Safe professional.