Overview
E167 on a Baxi Duo-tec / Megaflo indicates a fault related to the boiler’s printed circuit board (PCB) or an internal communication/sensor issue that the PCB has detected. The PCB monitors sensors (temperature, flue thermistor, flame sensor), fan, gas valve and other electrical components; if it sees inconsistent signals, water damage, wiring faults or internal electronic errors it will lock the boiler out and show a PCB-related code. Severity ranges from an inconvenient loss of heating and hot water to a safety lockout that prevents the boiler from firing until the problem is resolved. Some causes are electronic age or PCB failure, water ingress or corrosion on the PCB, broken/loose wiring or connectors, faulty sensors (flue, temperature or flame sensor), ignition/gas valve faults, or a blocked flue affecting sensors. A few simple checks and a reset may clear temporary faults, but because the PCB controls gas and ignition and diagnostic steps can require live electrical and gas isolation, most troubleshooting beyond visual checks and resets should be carried out by a qualified Gas Safe engineer. Attempting repairs to gas or PCB components without the right qualifications is unsafe and illegal in many jurisdictions.
Possible Cause: Printed circuit board (PCB) error
Troubleshooting Steps
Safety precautions:
- If you smell gas, do not operate the boiler. Turn off the gas supply at the meter, ventilate the area, leave the building and call the gas emergency number immediately.
- Turn the boiler off at the isolator switch and unplug or isolate electrical supply before removing panels or touching internal components.
- If you are not trained and registered (Gas Safe in the UK or equivalent), do not attempt to repair gas components, replace the PCB, or work on live wiring. Only perform non-invasive checks.
Initial checks a homeowner can do:
1. Record the fault code(s) and any display messages or flashing patterns. Take photos of the display.
2. Try a simple reset: press and hold the reset button (or follow the boiler manual) for 5–10 seconds. Wait for the boiler to attempt restart. Do not perform repeated resets more than a couple of times.
3. Check system water pressure on the gauge—aim for about 1–1.5 bar. Top up if pressure is low, following the boiler manual for filling the system.
4. Check external flue terminal for obvious obstructions (bird nests, debris). Do not climb or remove obstructing material yourself if it requires working at height—call a pro.
5. Visually inspect the boiler exterior and underside for signs of leaks or water on the appliance and around the PCB area (visible corrosion, damp patches). If you find water damage, switch the boiler off and call a engineer.
6. Ensure external controls, timers and room thermostat have power and are calling for heat as expected.
More detailed diagnostic steps (qualified person recommended):
1. Power and grounding: verify correct mains polarity, a secure earth and a dedicated circuit back to the distribution panel. Poor grounding can cause internal faults.
2. Visual PCB inspection: with power isolated, remove the front panel and check the PCB for burn marks, corrosion, moisture residue, swollen components or loose connectors. If water or corrosion is present, PCB replacement is commonly required.
3. Wiring and connectors: check all plug-in connectors and harnesses for secure seating and damaged wires. Re-seat connectors and inspect crimped joints.
4. Sensors and flame checks: measure sensor resistances and flame current as per the service manual. Sensors should read within the specified chart tolerance (±10%). Typical checks referenced in Baxi guidance: flame ionisation current should be about 3–5 µA when burning; if no microamp reading, clean/inspect flame sensor and wiring.
5. Gas valve coil resistance: using a multimeter, check gas valve coils if instructed by the manual. Example reference (from Baxi guide): pin 1–3 coil ≈ 20–30 Ω, pin 2–4 coil ≈ 60–70 Ω. If you get no Ohm reading, the gas valve may be faulty; if coils read correctly and wiring is good, the PCB may be at fault.
6. Ignition checks: check spark electrode condition, electrode gap and wiring to the PCB. Confirm adequate gas pressure/flow. If there is no spark or no flame signal and other components measure OK, the PCB may be responsible.
7. Flue thermistor and fan: test thermistor resistances and fan wiring. A blocked flue or fan failure can trigger PCB errors—inspect fan operation and flue path.
8. Temporary faults: if components test within spec but the code persists, remove power for at least 20 minutes, then reconnect and re-test. On some PCB replacements you must transfer the memory stick or easy-key and configure PCB parameters correctly—ensure any replacement PCB is programmed per Baxi instructions.
When to call a professional:
- If the error returns after a reset, if you find water damage, burnt components, or if any measurements are out of specification.
- For any checks or repairs involving gas valves, PCB replacement, solder joints, or live electrical tests.
- If the flue needs clearing at height or the fan needs replacement.
Final notes:
- Do not attempt to replace or reprogram the PCB unless you are a qualified engineer. PCB replacement often requires transferring a memory stick/easy-key and setting parameters; incorrect installation can leave the boiler unsafe or non-compliant.
- Provide the engineer with the recorded fault code(s), what checks you have already done, and any photos you took. This speeds diagnosis and repair.
- If you ever smell gas or suspect a dangerous fault, isolate and call the emergency gas service immediately.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Duo-tec/Megaflo.