Error E9 318

{ "ai_overview": "E9 318 on a Worcester Bosch GB162 indicates the boiler has detected an interruption in the flue gas temperature sensor circuit (the sensor contacts are open or disconnected). The flue gas temperature sensor is a safety device that monitors the temperature of the combustion/flue gases; if the control sees an open circuit or out‑of‑range value it triggers an E9 fault to stop the boiler. On some Worcester models E9 also covers high temperature / high limit trips or flue thermostat overheating, so the cause can be either a sensor wiring fault, a failed sensor, or an underlying overheating condition.\n\nSeverity: this is a safety shutdown. The boiler has locked out to prevent unsafe operation, so you should not ignore it. In many cases the fault is not immediately dangerous to read about, but it does mean the boiler will not operate normally until the problem is fixed. Homeowner actions are limited: you can try basic, non‑intrusive checks and a reset, but diagnosing and repairing faulty sensors, wiring inside the casing, or combustion/heat‑exchanger issues requires a Gas Safe registered engineer.\n\nDIY or professional: try simple external checks first (reset, visual inspection of the flue outlet and obvious wiring/connectors) but do not open the boiler casing, work on gas or combustion parts, or attempt component replacement unless you are a qualified engineer. If the fault persists after basic checks, call a Gas Safe engineer to investigate and repair.", "troubleshooting": "Safety precautions:\n1) If you decide to inspect anything, isolate the electrical supply to the boiler at the fused spur or mains switch before touching or removing any covers. Do not attempt to work on gas or combustion parts unless you are Gas Safe registered. Be aware that a faulty flue or combustion parts can risk carbon monoxide; if you suspect a flue or combustion fault stop using the appliance and get an engineer.\n2) Always keep children and pets away while carrying out checks. If you smell gas, evacuate and call the gas emergency number immediately.\n\nInitial homeowner checks (safe, non-intrusive):\n1) Make a note of the fault code exactly as shown (E9 318) and any other displayed cause codes or flashing indicators. Note when it occurred (e.g. during heating, after extended use, on start-up).\n2) Try a reset: press and hold the boiler Reset button for about 5 seconds (GB162 manuals reference ~5 seconds). Wait 2–3 minutes for the boiler to attempt restart. If the boiler clears and runs normally, monitor it for recurrence — persistent or recurring E9 faults require an engineer.\n3) If the fault returns immediately or shortly after resetting, switch the boiler off for 10–15 minutes to allow it to cool, then attempt a single reset again. Do not repeatedly reset the boiler if the fault reappears.\n4) Visually check the external flue terminal outside the building for obvious blockages (bird nest, leaves, debris) and remove only external obstructions safely. A blocked flue can cause high flue temperatures and trips. Also check that the condensate pipe (if external) is not frozen or blocked in cold weather.\n5) Check for obvious water leaks, loss of system pressure or warning lights on the boiler; note flow temperature shown on the display if available. Excessive CH flow temps or low system flow can indicate circulation problems causing overheating.\n\nWhat a Gas Safe engineer will do (diagnostic and repair steps they will follow):\n1) Access the boiler information menu/cause code (press the spanner/return as required) to confirm the cause code (318) and any related logged faults.\n2) Isolate power and gas, remove casing and perform a visual inspection of the flue gas temperature sensor, its connector and wiring harness for corrosion, loose pins, chafing, or water ingress. Repair or reseat connectors if required.\n3) Measure the sensor with a multimeter: check resistance/NTC behaviour at ambient temperature and while warmed (compare to manufacturer values) and check for open circuit or short circuit. If the sensor is open or out of spec replace the flue gas temperature sensor.\n4) Check continuity of the wiring from the sensor to the control board and inspect the control board connector for damage or burnt contacts. Repair wiring or replace the control board if the board is faulty.\n5) Investigate causes of high flue temperature that might have caused the circuit to trip: check pump operation and flow through the heat exchanger, check for blocked heat exchanger, scaling/limescale or flow restrictions, and verify correct flow/return temperatures. If overheating symptoms are present these must be addressed (pump service/replacement, flush or descaling, heat exchanger inspection or repair).\n6) Test the high limit thermostat / safety temperature limiter and replace if faulty. Confirm the boiler’s safety circuits and reset procedure work correctly after repair.\n7) After any repair the engineer will reset the boiler, verify correct ignition and firing, monitor flue and flow temperatures under load, and run the system to ensure the fault does not recur.\n\nWhen to call a professional and final notes:\n1) Call a Gas Safe registered engineer if the E9 318 fault does not clear after the simple external checks and one or two controlled resets, or immediately if you suspect the flue is blocked, you detect leaks, or you are not competent to isolate and inspect electrical/gas components.\n2) Do not repeatedly reset the boiler without diagnosing the cause; persistent trips indicate a real safety issue. Provide the engineer with the exact fault code(s), how often it occurs, any conditions when it happens (e.g. under high load), and what you have already tried.\n3) Keep the boiler off if you suspect combustion/flue faults or if you cannot ensure safe operation. Only a qualified engineer should open the boiler, test sensors and wiring, and replace components.