Overview
E168 on a Potterton Promax boiler means the printed circuit board (PCB) has gone into lockout. The PCB is the boiler’s control board; a lockout indicates the board has detected a repeated or serious fault and has shut the boiler down to protect safety-critical systems (gas, ignition, overheat, fan, sensors). The lockout is the board refusing to allow normal operation until the underlying cause is fixed and the lockout is cleared. This is a high-severity fault because it involves the boiler’s control electronics and safety interlocks. Some causes are internal PCB failure, repeated ignition or flame loss events that forced the board to lock out, voltage or supply problems, water damage to the PCB, or persistent faults elsewhere (fan, sensors, circulation) that the PCB has used as a reason to lockout. Basic checks and a reset are reasonable for a competent homeowner, but diagnosing and repairing PCB faults, replacing the PCB, or anything involving the gas supply must be done by a Gas Safe registered engineer. Do not bypass lockouts or attempt major PCB repairs yourself.
Possible Cause: Printed circuit board (PCB) lockout
Troubleshooting Steps
Safety precautions:
- If you smell gas or suspect a gas leak, leave the property immediately and call the gas emergency number. Do not operate electrical switches or the boiler.
- If the boiler is locked out, switch the boiler to the Off position and isolate electrical power at the fused spur if safe to do so. Do not remove the boiler casing or work on gas components unless you are Gas Safe registered.
- Keep children and pets away while you check the boiler. If you see water on or around the PCB, switch the boiler off and call an engineer.
Initial checks a homeowner can safely do:
1. Note the exact error code and any other codes shown before or after E168 (for example E133, E110, etc.). Also note when it happened and any recent changes (power cuts, storms, servicing, freezing weather).
2. Try a controlled reset: follow the boiler manual - typically press and hold the reset button for 3–5 seconds. Wait to see if the boiler starts normally or returns to E168 or another code.
3. Check the mains power: verify the boiler switch is on and the fused spur or RCD has not tripped. Check other appliances to confirm household power is present.
4. Check system pressure: look at the pressure gauge on the boiler. If pressure is very low (typically below about 0.8–1.0 bar) repressurise to the manufacturer’s recommended pressure (often ~1.0–1.5 bar) following the manual. If unsure, do not attempt complicated filling loop procedures—call an engineer.
5. Check gas supply: ensure other gas appliances (hob, gas fire) work. If there’s no gas supply, contact your supplier or a registered engineer.
6. Visual inspection: with power isolated and the outer case closed, visually check around the boiler for leaks, obvious burn marks, scorched wiring, a damp smell, or water on the casing. If you find corrosion or water ingress near the PCB, switch off power and call a Gas Safe engineer.
Specific diagnostic and next steps (homeowner level):
1. Record history: keep a note of when the fault started, any patterns (only on ignition, only in cold weather), and any other error codes that appeared immediately before E168 (for example E133 ignition faults). This helps the engineer.
2. Reset once: if a reset cleared the fault and the boiler runs normally, monitor closely. If the lockout returns repeatedly, stop resetting and call a professional—repeated resets can mask an underlying safety issue.
3. Check for simple external causes: frozen condensate pipe in cold weather, blocked flue vents, or recent power surges can trigger faults on occasion. Thaw a frozen condensate pipe if safe to do so (warm water on the outside of the pipe) and retest. Do not heat the pipe with open flame or hot objects.
4. Do not attempt PCB repairs or replacements yourself. Do not short out safety circuits or bypass interlocks to force the boiler to run.
When to call a professional and what to tell them:
- Call a Gas Safe registered engineer if E168 persists after a single reset, or at any time you see signs of water damage, burning, persistent ignition failures (E133), fan faults, or other repeated lockouts. Also call if you are not comfortable performing the basic checks above.
- When you contact the engineer, give them: boiler model and serial number, exact error code(s) (E168 and any others that appeared), what you have tried (resets, pressure check, gas supply check), the pressure reading, and any visual signs (leaks, scorch marks, smell of burning).
What the engineer will typically do (for your information):
- Run electrical tests: verify correct mains voltage, check fuses and the boiler isolator, and inspect wiring and connectors to the PCB.
- Read the full fault history and replicate fault conditions to identify upstream causes (ignition, fan, sensors, circulation faults) that led to the lockout.
- Inspect the PCB for signs of water damage, corrosion, burned components, or failed solder joints. Check sensor inputs, fan operation, gas valve, and ignition system.
- Replace the PCB only if faulty or damaged, and restore correct settings. Perform safety and ignition tests before returning the boiler to service.
Final note:
E168 is a control-board lockout and should be treated as a significant fault. Limited homeowner troubleshooting (reset, pressure, supply checks, and safe visual inspection) is acceptable, but do not attempt PCB repairs or gas work. If the fault persists or if you find signs of damage or water ingress, switch the boiler off and arrange a Gas Safe engineer or the manufacturer service. If the appliance is under warranty, contact the installer or manufacturer before arranging third-party repairs.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Potterton Promax Combi, System, and Store.