Error E135

Safety first

1. If you smell gas or suspect a leak: do not operate switches, do not use phones inside the building. Get everyone out immediately and call your local gas emergency number from a safe location (in the UK, 0800 111 999). If you can do so safely, turn off the gas supply at the meter and do not return until a qualified professional has declared it safe.

2. If there is no smell of gas, proceed with caution and do not attempt to open or repair gas components yourself. Only visual and simple non-invasive checks are safe for a homeowner.

Initial checks a homeowner can do

1. Check other gas appliances (hob, oven, gas fire) to see if they are working. If none work, the issue is likely a broader gas supply problem or meter/prepay credit.

2. Check your gas meter and prepayment status. Ensure you have credit and the meter hasn’t tripped an emergency control. If the meter has an emergency control, follow the supplier instructions to reset it.

3. Locate the gas isolation valve to the boiler (a lever or key under the boiler pipework) and confirm it is in the open position. Do not turn it on or off repeatedly.

4. Check the boiler pressure gauge. Although E135 is a gas interruption fault, very low water pressure can also prevent normal operation. Aim for roughly 1.0–1.5 bar when cold. If pressure is low, you can top up using the filling loop following the manufacturer instructions, then try a reset.

5. In freezing weather, check the condensate pipe (external plastic pipe) for ice. If frozen, thaw it with warm water (not boiling) or a warm cloth; do not use naked flames or heaters directly on the pipe.

6. Check that external flue terminals and air vents are not blocked by debris, birds, or snow.

Reset procedure (homeowner)

1. Find the boiler reset control (button with a flame symbol or selector marked R or Reset). Follow the user manual for your exact model.

2. Press and hold the reset for about 5–10 seconds, then release. The boiler will attempt to re-light.

3. Watch the display and listen: if the boiler lights and runs normally, monitor for recurring faults for the next 24 hours.

4. Do not keep repeatedly resetting the boiler if the code returns. One or two attempts is reasonable; repeated resets can cause additional problems and are discouraged.

When to call a professional

1. If you smelled gas at any time, call the gas emergency service immediately and then a Gas Safe registered engineer — do not attempt repairs.

2. If other gas appliances are dead and the meter/credit and isolation valves are correct, you need your gas supplier or a Gas Safe engineer to investigate the supply.

3. If the E135 reappears after a proper reset, or if the boiler attempts ignition but fails (or displays additional error codes), stop trying to reset and book a Gas Safe registered engineer. This can indicate a faulty gas valve, ignition transformer, flame probe, PCB or wiring fault that requires specialist testing and parts replacement.

4. If you have to thaw a condensate pipe regularly in cold weather, consider insulating the pipe or having an engineer apply a more permanent solution.

What the engineer will check (for your information)

A qualified Gas Safe engineer will check the incoming gas pressure, the boiler isolation valve, ignition components, flame detection electrode, gas valve operation, wiring and PCB fault logs, and perform combustion and safety tests. They will only undertake repairs or replacements after diagnosing the exact cause.

Notes and what to tell the engineer

1. Note the exact error code (E135) and any other codes or lights shown when the fault occurred, and how many reset attempts you made.

2. Tell the engineer whether other gas appliances work, whether you smelled gas, whether you have a prepayment meter, and whether the problem started after any works or a power outage.

Summary

Do the basic checks and a single reset only if there is no smell of gas. If the fault persists, repeats, or if you smell gas, stop and call a Gas Safe registered engineer. Do not attempt internal gas repairs yourself.