Error E135

Safety precautions:

1. If you smell gas: do not operate electrical switches, do not light any naked flames, ventilate the property by opening windows and doors, evacuate occupants, and call your local gas emergency number or gas supplier immediately. Do not attempt any internal repairs.

2. If you do not smell gas, still proceed cautiously. Turn the boiler off at the mains before inspecting any external controls. Never open the boiler casing or access gas/ignition components yourself.

Initial homeowner checks (safe checks you can do yourself):

1. Note the exact error code and whether it clears or reappears after a reset. Count how many resets you do and record times — this helps the engineer diagnosis.

2. Check other gas appliances in the property (cooker, gas fire, gas hob). If they are also not working, this strongly suggests a supplier or meter/isolation issue rather than a boiler internal fault.

3. Check the gas meter and external isolation valve if accessible: ensure the meter isolation lever is in the ON position. If you find the meter has been turned off and you are unsure why, contact your gas supplier.

4. Check the boiler’s system pressure on the gauge (low pressure can cause ignition problems). If pressure is very low (below manufacturer's recommended level, typically ~1–1.5 bar), you can top up using the filling loop following the manufacturer instructions — only if you are confident and have done this before.

5. Check for frozen pipes or frozen condensate discharge in cold weather; a blocked condensate can cause various faults. Thaw gently with warm (not boiling) water if you suspect freezing.

6. Try a controlled reset: switch the boiler off, wait 30 seconds, switch back on and press the reset button per the manual. If the code clears and the boiler runs normally, monitor for recurrence.

Specific diagnostic steps and what to expect:

1. If other appliances don’t work: call your gas supplier to check for outages, meter issues, or supply interruption. If the supplier confirms supply is OK, note the reference and proceed to the next step.

2. If other appliances work but the boiler still shows E135 after reset: do not attempt internal repairs. Power-cycle the boiler once (turn off at the mains for 1 minute then on) and try reset per manual. If E135 returns immediately or after a short time, this suggests an internal detection of interrupted gas or electronic/gas valve fault.

3. Inspect visible external wiring and connectors to the boiler (only externally accessible terminals): look for loose connectors, water ingress, or obvious damage. Do not remove covers or touch internal PCB or gas valve connections.

4. Check the fault history if your boiler displays it or in the user manual instructions — frequent repeated lockouts or codes accompanying E135 (like E133, E134, flame failure codes) are important to report to the engineer.

5. If the boiler indicates low voltage or other electrical warnings alongside E135, ensure the supply to the property is stable. Persistent low voltage requires an electrician or your supplier.

When to call a professional and what to tell them:

1. Call a Gas Safe registered engineer if the E135 persists after the safe checks above, if other gas appliances work but the boiler does not, or if the boiler locks out repeatedly. Do not attempt to access or repair gas valves, burner, PCB, or ignition components yourself.

2. If you smell gas, evacuate and call the gas emergency service immediately before calling an engineer.

3. When you contact the engineer, provide: boiler make/model, serial number if available, the exact fault code (E135), a timeline of events, results of your checks (other appliances working, supply checked with supplier, number of resets), and any accompanying codes or behaviour (repeated lockouts, noises, pressure readings).

Final note: E135 can be caused by legitimate temporary supply interruptions and may clear once supply is restored, but because it involves gas supply and internal detection it should be treated seriously. For safe diagnosis and repairs, always use a Gas Safe registered engineer.