Error E15

Safety precautions:

- If you smell gas, evacuate the property immediately, call the emergency gas service/your gas supplier or 999 depending on your local emergency procedure, and do not operate any electrical switches or appliances.

- Before opening the boiler or touching internal parts, switch the boiler off at the control and isolate the mains supply at the consumer unit. If you will be isolating the gas supply, turn the gas service cock off. Only a Gas Safe engineer should work on gas fittings or perform leak tests.

- If you are not comfortable with electrical isolation or working near gas components, stop and call a Gas Safe engineer.

Initial homeowner checks you can do safely:

1) Note the exact error code, any other codes or LEDs, and take a photo of the display and the boiler label (model/serial). This helps the engineer.

2) Try a single controlled reset using the boiler’s reset procedure. If the fault clears and does not return, monitor for recurrence. Do not continuously reset more than once or twice if it relocks immediately.

3) Check that the boiler has power (other appliances on the same circuit working) and that external controls (room thermostat, programmer) are calling for heat. Ensure gas supply to the house appears normal: check other gas appliances (hob, gas fire) if safe to do so.

4) Visually inspect any external wiring you can see (room thermostat cable, external controls, and the boiler’s visible wiring entries). Look for loose cable glands, damaged or chewed cables, water ingress or corrosion. Do not open the boiler casing unless you are competent and have isolated mains power.

5) If the boiler has been recently serviced, worked on, or vibrated, check that connectors and terminal screws on the outside of the unit are secure.

Diagnostic and fix steps for an engineer or competent person (do not perform unless qualified):

1) With mains power isolated, remove the boiler casing and visually inspect the gas valve connector(s), the wiring harness, and the PCB connector for loose pins, corrosion, overheating marks or cracked insulation. Re-seat connectors and replace any visibly damaged connector housings or wires.

2) With appropriate test equipment and following safe isolation and PPE procedures, check continuity of the gas valve wiring back to the PCB and check for short circuits to earth. Measure gas valve coil resistance and compare to the manufacturer specification. If the coil is open or out of spec, replace the gas valve.

3) With the boiler powered and under controlled conditions, measure the control voltage/signals from the PCB to the gas valve during an ignition sequence to confirm the PCB is commanding the valve and that the valve is responding. If the PCB supplies the correct command but the valve does not operate, the valve is at fault. If the valve is healthy but no command is present, suspect the PCB or wiring/connector between them.

4) Inspect the PCB for damaged components, dry joints, burnt traces or evidence of moisture ingress. Repair or replace the PCB only with the correct replacement part following manufacturer guidance.

5) Check for related causes: moisture/condensate on connectors, pest damage to wiring, recent overheating events, or external controllers causing spurious commands. Replace or protect wiring as required.

6) After any repairs, restore gas and electrical supplies safely, perform a controlled ignition and run the boiler through a full sequence. Confirm no gas leaks (engineer must perform an appropriate gas-tightness check) and observe for any repeat of the E15 fault.

When to call a professional:

- If the E15 code persists after a single safe reset, or if it returns repeatedly, call a Gas Safe registered engineer. Anything that requires access to the gas valve, internal wiring, PCB testing, or gas-tightness checks must be carried out by a qualified professional.

- If you find damaged wiring, burn marks, a suspected faulty PCB or a suspected leaking/failed gas valve, isolate the appliance and book an engineer immediately.

Other notes:

- Record dates, times, and any actions taken (resets, checks) and provide this information to the attending engineer. Photographs are useful.

- Repeated lockouts should not be ignored; they indicate an unsafe or unreliable condition. Prioritise a Gas Safe visit rather than repeated DIY attempts.