Cooker
F04
The F04 error code on a Smeg cooker indicates a fault with the oven temperature sensor (NTC probe), meaning the appliance cannot accurately read or regulate the oven cavity temperature. It’s a moderately serious fault — your oven will likely stop heating or refuse to start until it’s resolved.
What does this error mean?
The F04 code tells you the oven’s internal temperature sensor (known as an NTC or thermocouple probe) is sending a reading that’s outside the expected range — either an open circuit, short circuit, or a completely absent signal. Smeg’s control board uses this sensor to manage heating element power and keep the oven at the correct temperature. Without a reliable reading, the oven locks out as a safety measure to prevent overheating or underheating your food.
Est. repair cost
£15–£35 DIY NTC sensor replacement; £80–£150 professional repair (sensor + labour); £150–£280 if control board replacement is required
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 – Reset the oven: Switch the cooker off at the wall socket, wait 5 minutes, then switch back on. If F04 clears, monitor closely — a one-off glitch can occur after a power surge.
Step 2 – Check for obvious spillage near the sensor: Open the oven and look at the rear wall or roof for the small metal probe (usually a thin rod with a wire attached). If it’s coated in burnt food or grease, carefully clean around it with a damp cloth once the oven is completely cool — do not use caustic sprays directly on the probe.
Step 3 – Inspect the sensor wiring: With the oven unplugged at the wall, gently trace the wire from the NTC probe toward the back of the oven. Look for any visible damage, scorching, or a connector that has come apart. Reseat any loose connectors firmly.
Step 4 – Test the NTC sensor resistance (if you have a multimeter): A healthy Smeg NTC sensor typically reads around 900–1,100 ohms at room temperature (20°C). Disconnect the sensor connector and test across the two terminals. A reading of 0 (short) or OL (open circuit) confirms the sensor has failed and needs replacing.
Step 5 – Replace the NTC sensor: Smeg NTC oven sensors are widely available from UK appliance parts suppliers (e.g. 4ourhouse, eSpares) for £15–£35. The sensor is usually held in place by one or two screws on the oven interior wall — unscrew, unplug the connector, fit the new sensor, and reconnect. Ensure it’s a part confirmed compatible with your exact Smeg model number.
Step 6 – If replacing the sensor does not clear F04: Stop here. A persisting F04 after a confirmed sensor replacement points to a control board fault, which requires a qualified appliance engineer to diagnose and repair safely.
📞 When to call a professional
Call a qualified appliance repair engineer if the F04 error persists after you’ve replaced the NTC sensor, or if you find scorched wiring inside the oven cavity that you cannot safely trace. Tell the engineer: ‘My Smeg oven is showing error code F04 — I believe it’s an NTC sensor or PCB fault.’ If your appliance is a Smeg dual-fuel cooker with a gas hob, any work on the gas components must be carried out by a Gas Safe registered engineer only.
⚖️ Repair or replace?
A professional repair for F04 — covering diagnosis, an NTC sensor, and labour — typically costs £80–£150 at UK market rates; a control board replacement can push this to £150–£280. If your Smeg cooker is under 8 years old, repair is almost always worthwhile given Smeg’s premium build quality and the relatively low cost of an NTC sensor. If the appliance is over 10–12 years old and the control board has failed, replacement with a comparable range cooker may be more cost-effective in the long run.