Error E135

Safety precautions:

- If you smell gas: stop using gas appliances, do not operate electrical switches, ventilate the property, leave the building and call the national gas emergency number immediately. Do not attempt any repairs.

- If you do not smell gas, still exercise caution: do not open the boiler case or touch internal components unless you are a qualified engineer. Isolate electrical supply at the fused spur if doing visual checks around the boiler.

Initial homeowner checks (safe, non-intrusive):

1. Record the code and behavior: note when E135 appeared, whether heating, hot water or both are affected, and take a photo of the display for the engineer.

2. Check other gas appliances: try the hob or gas fire to see if they work. If all gas appliances are dead, suspect a gas supply interruption and contact your gas supplier.

3. Check the boiler pressure gauge: note the pressure. Although E135 is not usually a pressure fault code, extremely low pressure can cause other faults—top up to around 1–1.5 bar only if you know how and there are no leaks.

4. Check the mains electrical supply: has a fuse blown at the consumer unit, or has an RCD/MCB tripped? Restore safely if you are familiar with your fuse box.

5. Reset the boiler once: press and hold the boiler reset button as per the manual (typically 3–5 seconds). If the fault clears and the boiler runs, monitor it. If E135 returns, do not repeatedly reset—limit attempts to avoid masking a dangerous intermittent fault.

6. Power-cycle the boiler: switch off at the boiler isolated spur or fused switch for 30 seconds and turn back on, then observe the display.

Specific diagnostic guidance and next steps (what an engineer will do / what you should expect):

- If gas supply is confirmed interrupted at your property (no hob, neighbour unaffected), contact your gas supplier. If the supplier confirms supply is OK but the boiler still shows E135, the fault is internal.

- If electrical supply issues were identified (tripped breaker, low voltage), a stable mains supply will be required before the boiler can be trusted to run. An electrician or Gas Safe engineer may be needed to verify acceptable voltage levels.

- If E135 persists after supply and simple resets, the likely causes include PCB/control electronics fault, gas valve/ignition circuitry fault, or internal communication/interruption. These require diagnostic tools, safe access to the boiler internals, and replacement or repair of components by a Gas Safe registered engineer.

- When calling an engineer, give them: boiler model, serial number if available, exact fault code (E135), any other codes or lights shown, what you tried (reset, power-cycle), whether other gas appliances are working, and whether there was any smell of gas.

Important homeowner warnings:

- Do not attempt to repair or replace gas valves, wiring, PCBs, ignition components or any internal parts yourself. Working on gas and sealed electrical parts is dangerous and illegal if you are not Gas Safe registered.

- Limit resets to a couple of attempts. Persistent lockouts need professional investigation rather than repeated resets.

When to call a professional:

- Call a Gas Safe registered engineer whenever E135 does not clear after the basic checks above, or sooner if you smell gas, see signs of burning, smell electrical burning, or the boiler shows additional fault codes. The engineer will perform safe diagnostics, check gas and electrical supplies, read service logs, and carry out remedial repairs or replace faulty components as required.