Overview
E168 on Baxi Duo-tec / Megaflo boilers is a PCB lockout fault. In plain terms the boiler control board has detected a problem it can’t resolve and has locked the boiler out to protect the appliance. E168 is a generic symptom rather than a single specific failed part — it commonly appears after the boiler has already shown other, more specific error codes, or when the control board itself has experienced an electrical fault, intermittent mains supply, or water damage. Why it happens: there are four main causes seen in the field: 1) the boiler previously displayed another fault (E20, E28, E50, E110, E119, E125, E130, E133, E156, E160, etc.) and a reset removed the original code but left the board in lockout; 2) unstable or incorrect mains voltage (outside about 230V ±10%); 3) a related component is failing or has lost electrical integrity (gas valve, spark igniter, electrodes, pump, fan, diverter cartridge, sensors, wiring); 4) the PCB itself has failed or been damaged (commonly by water or corrosion). Severity and who should act: E168 is a high-severity fault because it prevents the boiler operating and can indicate electrical faults or water ingress to electronics. Basic visual and non-invasive checks can be done by a competent homeowner, but electrical, gas and internal fault-finding must be performed by a qualified Gas Safe engineer (and an electrician for mains supply issues). Avoid repeated resets — that can mask the root cause or cause further damage.
Possible Cause: Printed circuit board (PCB) lockout error
Troubleshooting Steps
Safety first
- If you smell gas, immediately evacuate the property and call the national gas emergency number. Do not operate electrical switches or the boiler.
- Switch off the boiler at the external fused spur or isolation switch before doing any inspection.
- If you find water inside the casing or obvious electrical corrosion, isolate power and call an engineer. Do not attempt internal repairs unless you are a Gas Safe registered engineer.
- Do not repeatedly reset the boiler. One controlled reset is acceptable; repeated resets can cause further damage.
Initial checks a homeowner can do (non-invasive)
1. Note the display: write down E168 and any other codes you saw previously or that appear briefly before E168. Previous codes are often the root cause.
2. Check boiler pressure: the cold system pressure is normally about 1.0–1.5 bar on most Baxi systems. If pressure is clearly low, you can re-pressurise following the manufacturer’s filling-loop instructions in the handbook, but only if you are confident. Avoid overfilling.
3. Power supply basics: check the boiler fused spur, the consumer unit (tripped MCB or RCD) and whether other appliances on the same circuit work. If the home has recent power cuts or tripping, note it.
4. Visual inspection of the outside and casing: look for obvious signs of water ingress (staining, damp, pooling on top of the casing, visible corrosion around flue or gland areas). If you see water inside the cabinet or obvious leaks, turn off power and call an engineer.
5. Condensate pipe: in cold weather a blocked/frozen condensate can cause ignition faults — check the external condensate discharge is clear and not frozen or blocked (but don’t dismantle internal plumbing).
6. Single controlled reset: switch the boiler off at the fused spur for 30 seconds, then switch on and try to restart. If E168 returns immediately or the boiler will not run, stop and call a professional.
If the fault persists — what an engineer will (or should) check
1. Retrieve any logged/previous error codes and service history. Investigate the root codes if present (E20/E28/E50 = sensor issues; E119 = low pressure; E125/E130 = over-temperature/circulation or flue problems; E133 = ignition failure; E156 = low incoming voltage; E160 = fan).
2. Mains and earth tests: measure incoming voltage and verify supply is within tolerance and properly earthed. If mains voltage is outside tolerance or intermittent, involve a qualified electrician and the supply company.
3. Inspect for water ingress and corrosion: check the PCB for moisture, brown scorch marks or corrosion. Look for leaks from condensate traps, pressure sensor areas, auto air vents, or split internal piping that could have dripped onto electronics.
4. Check wiring and connectors: verify harnesses, plugs and earths are clean and secure; replace or repair corroded connectors.
5. Test ignition circuit and components: check spark generator, electrodes (gap and condition), gas valve coils and wiring. Replace faulty spark generator/electrodes if needed.
6. Check fan operation and flue NTC/temperature sensors; replace or repair as required.
7. Test pump, pressure switch and diverter valve operation (sticking diverter cartridges are common and can cause related faults).
8. Verify sensors and thermistors (boiler temperature NTCs, flue NTC, DHW NTC) are within expected readings and wiring intact.
9. After isolating and repairing any failed component, clear the fault and run a full commissioning sequence and safety checks (gas rate, CO, combustion where applicable).
10. If all subsystems test good and fault returns, replace the PCB with the correct manufacturer part and re-test. A PCB replaced without investigating root causes can fail again if water or a shorted component caused the original failure.
When to call a professional and escalation
- Call a Gas Safe registered engineer whenever internal electrical/gas components need testing, or if you see water inside the casing, corrosion or cannot resolve the fault after the non-invasive checks.
- For suspected supply voltage instability call a qualified electrician and inform your electricity supplier if required.
- If the boiler is under warranty contact the manufacturer or installer first.
Final notes
- E168 is a protective lockout and often points to an underlying fault; do not ignore it.
- Keep a record of observed error codes, times and any power events to help the engineer diagnose intermittent supply issues.
- Only a qualified Gas Safe engineer should carry out internal repairs, gas valve or PCB replacements and full electrical checks.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Duo-tec/Megaflo.