Boiler
168
Error code 168 on a Potterton boiler signals a fault with the external controls or room thermostat wiring circuit — it’s not an emergency, but it will prevent your boiler from firing until it’s resolved.
What does this error mean?
The 168 fault code indicates that the boiler’s control board is detecting an open circuit or a missing signal from an external control device — typically a room thermostat, programmer, or smart thermostat. The boiler is essentially waiting for a valid ‘call for heat’ signal that isn’t arriving. This is a controls/wiring issue, not an internal boiler component failure in most cases.
Est. repair cost
£80–£180 for thermostat/wiring fix; £300–£500 for PCB replacement (all costs include Gas Safe engineer labour)
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Reset the boiler: Press and hold the reset button for 3–5 seconds, then release. Wait 60 seconds to see if the boiler fires normally. If it does, monitor for recurrence.
Step 2 — Check your thermostat is powered and set correctly: Ensure the room thermostat is calling for heat (set it above current room temperature), has working batteries if wireless, and its display is active.
Step 3 — Check your programmer or timer: Confirm it is set to a heating ‘on’ period and that its fuse (typically 3A) hasn’t blown. Replace the fuse if needed — this is a safe DIY task.
Step 4 — Inspect external wiring connections (only if confident with low-voltage wiring): With the boiler and controls powered off at the fuse spur, check that the wires at the room thermostat terminals and the boiler’s external controls terminals (often marked ‘LS’ or terminals 3 & 4) are firmly seated and not corroded. Do NOT open the boiler casing.
Step 5 — If you have a smart thermostat recently installed: Check the manufacturer’s wiring guide to confirm it provides a switched live output to your boiler. Some smart thermostats require a Honeywell-style wiring configuration to signal the boiler correctly.
Step 6 — If the error persists after all of the above: Stop here. Do not attempt to open the boiler or interfere with gas components. Call a Gas Safe registered engineer.
📞 When to call a professional
Call a Gas Safe registered engineer if the boiler continues to display error 168 after a reset and after you’ve confirmed your thermostat and programmer are functioning correctly. Tell the engineer: ‘My Potterton boiler is showing fault code 168 — I believe it’s a controls or external wiring issue.’ If you suspect the PCB is faulty, an engineer will need to diagnose and replace it — this is not DIY territory.
⚖️ Repair or replace?
A controls wiring fix or thermostat replacement typically costs £80–£180 including labour; a PCB replacement on a Potterton boiler can reach £300–£500 fitted. If your boiler is over 10–12 years old and the PCB has failed, replacement with a modern A-rated boiler (from around £1,800–£2,500 installed) is likely more cost-effective long term. For boilers under 8 years old in otherwise good condition, repair is almost always the right call.