Error E128

Safety first

1) If you smell gas, stop using the boiler and any electrical switches, evacuate the property and call the gas emergency number immediately. Do not try to diagnose or restart the boiler if you suspect a gas leak.

2) If the boiler is locked out with E128, isolate electricity at the wall before doing any physical checks on the appliance.

Initial checks a homeowner can safely do

1) Check other gas appliances in the house to see if they are working — if they are not, it points to a supply or meter issue. If you have a prepayment meter, confirm there is credit.

2) Confirm the gas isolation valve to the property is fully open (if you know where it is and can safely check it).

3) Inspect external flues and air vents for obvious blockages (birds' nests, leaves, debris) from ground level only. Do not crawl into confined spaces or dismantle the flue.

4) Check the external condensate pipe (usually a small plastic pipe that runs to an outside drain). In cold weather this can freeze and cause repeated flame loss errors.

Simple remedial steps you can perform safely

1) If you suspect a frozen condensate pipe: turn the boiler off at the control panel and isolate electrical power at the wall. Locate the exposed section of condensate pipe (the most exposed/visible part) and gently warm it along its length using a hot water bottle, a microwaveable heat pack, or warm (not boiling) water poured slowly. Do not use open flame, blowtorches or boiling water as these can damage the pipe. Once thawed, restore power and restart the boiler following the manufacturer's reset procedure (press and hold the reset button or power/reset for around 5–10 seconds; consult your manual for exact steps). You may need to repeat warming and restarting until the boiler stays running.

2) If you cleared a frozen condensate pipe and the boiler runs again, consider insulating the condensate pipe or asking an engineer to reroute or fit trace heating to prevent recurrence.

3) If flue/external vent blockage was cleared, restart the boiler after restoring power. If the error clears, monitor for recurrence.

When to stop and call a professional

1) If initial safe checks (condensate thaw, checking external vents, confirming gas supply) do not clear the fault, or the boiler repeatedly locks out (many tries or the same E128 returns), do not continue to reset repeatedly. Repeated lockouts indicate a persistent fault needing diagnostic equipment and safe handling.

2) Call a Gas Safe registered engineer when you suspect gas supply problems, ignition or flame detection faults, blocked burners, internal components or if you are not comfortable performing the safe checks above. A qualified engineer will test gas pressure, inspect and replace ignition electrodes or flame sensors, clean or service the burner and flue, and check the condensate drain installation.

3) Never attempt internal repairs on gas valves, burners, electrodes, or the boiler PCB yourself. Only a Gas Safe engineer should perform these repairs.

Summary

1) E128 = repeated flame loss and safety lockout. 2) Start with safe external checks: gas supply, vents, and thawing/clearing the condensate pipe in cold weather, then reset once power is restored. 3) If the problem persists, or if you smell gas or see signs of serious malfunction, contact a Gas Safe registered engineer immediately.