Error 128

Safety precautions:

1) If you smell gas (rotten egg odor or strong gas smell) or suspect a leak, stop immediately: do not operate electrical switches, do not light matches or use naked flames, ventilate the area by opening doors/windows, leave the property and call the national gas emergency number immediately.

2) If the boiler is locked out with the 128 code, do not keep repeatedly pressing reset more than once or twice — frequent resets can be unsafe and may worsen a fault.

3) Always isolate electrical power at the wall to the boiler before touching any external parts. Do not attempt internal electrical or gas component work unless you are Gas Safe registered.

Initial homeowner checks you can safely do:

1) Check other gas appliances: confirm other gas appliances (hob, oven, gas fire) are working — this helps identify if there is a wider gas supply interruption.

2) Check gas meter and any external gas isolation (including prepayment card top-up status) to ensure the household gas supply is active.

3) Inspect external flue and air intakes: ensure vents or the flue outlet are not blocked by debris, bird nests, snow or leaves.

4) Check the condensate pipe: E128 can be triggered by a frozen or blocked condensate discharge, especially in cold weather. Look for exposed plastic pipe runs from the boiler to the drain outside that might be frozen.

5) Check boiler pressure: confirm system pressure on the pressure gauge is within normal range (typically about 1–1.5 bar when cold); very low pressure can cause other faults.

Safe reset procedure (do this only after the checks above):

1) Switch the boiler off at the control panel and isolate mains power at the wall for 30 seconds.

2) Turn the power back on and use the boiler reset button (or hold the power/reset as per your model instructions). Press and hold for the recommended time (usually around 5 seconds) and allow the boiler to attempt to relight once. If your model guidance mentions holding a button for 2 seconds after a specific sequence, follow the manufacturer instructions printed on the boiler.

3) If the burner lights and the boiler runs normally, monitor it for a while. If the fault returns, stop further resets and proceed to call a professional.

Condensate pipe thawing (if you suspect freezing):

1) Locate the external condensate pipe (typically small diameter plastic running to an outside drain).

2) Warm the pipe along its exposed length using warm (not boiling) water poured gently, a warm water bottle, or a warm heat pack. Do not use open flames or boiling water that could damage the pipe or injure you.

3) Once thawed, restore mains power and attempt the one controlled reset. Repeat warming if necessary until the boiler restarts.

If the boiler still shows 128 after these checks and a single reset, do not attempt internal adjustments:

1) Do not try to adjust the gas valve, ignition electrodes, flame sensor, or internal wiring unless you are a qualified Gas Safe engineer.

2) Note the exact error code, any other fault lights, conditions when the fault appears (e.g., only when heating, only on demand), and take a photo of the display and boiler rating/serial plate if possible.

3) Call a Gas Safe registered heating engineer and provide them with the code (128/E128), what checks you have already carried out, and any other symptoms (smells, noises, repeated lockouts). The engineer will carry out safe gas checks, flue and combustion tests, inspect ignition electrodes, flame detection, burner condition and condensate/drainage, and repair or replace faulty components as needed.

Final note: This fault concerns fuel ignition and combustion safety. If it does not clear with the simple, safe actions above, stop attempting further DIY fixes and arrange for a Gas Safe registered professional to diagnose and repair the boiler.