Oven
F12
The F12 error code on a Siemens oven indicates a fault with the oven’s temperature sensor (NTC sensor) or its connection to the control board — it’s a moderately serious fault that will prevent the oven from heating safely until resolved.
What does this error mean?
F12 signals that the oven’s electronic control system has detected an out-of-range or implausible reading from the temperature sensor (also called an NTC or thermocouple probe). In plain terms, the oven can’t confirm what temperature the cavity is reaching, so it shuts down as a safety precaution. This is an electrical fault, not a gas issue, and is specific to Siemens built-in and freestanding electric ovens.
Est. repair cost
£15–£40 DIY sensor replacement; £80–£150 professional sensor repair; £150–£300 if PCB replacement is needed
🔍 Likely causes
🛠️ Step-by-step fix
Hard reset the oven: switch it off at the wall socket (or trip the circuit breaker), leave it unpowered for 5–10 minutes, then switch back on. If F12 clears and doesn’t return, a power glitch was the cause — monitor closely.
Check the oven is not overheating from restricted airflow: ensure there is adequate clearance around the appliance and that the cooling fan vents (usually at the top or rear) are not blocked by foil, trays, or built-up grease.
Inspect the temperature sensor probe: it is typically a thin metal rod mounted on the back wall of the oven cavity, secured by one or two screws. With the oven fully unplugged, visually check for obvious damage, burning, or corrosion. A damaged probe is your likely culprit.
Test the NTC sensor resistance (if you own a multimeter): disconnect the sensor plug and measure resistance across the two terminals. At room temperature (~20°C) a healthy Siemens NTC sensor typically reads 4,000–6,000 ohms. A reading of zero or infinite resistance confirms a failed sensor.
Replace the NTC sensor: Siemens replacement sensors for common models cost £15–£40 online (search your full model number, found on the frame inside the oven door). Unplug the oven, unscrew the old probe, disconnect the spade connectors, connect the new one, and refit. No soldering required.
If the error persists after replacing a confirmed faulty sensor, stop DIY work — the control board (PCB) is likely at fault and requires a professional repair.
📞 When to call a professional
Call a qualified appliance engineer if F12 returns after a reset and you’ve confirmed the temperature sensor tests correctly, as the fault likely lies with the main PCB or a damaged wiring harness — both require professional diagnosis. When booking, tell the engineer: ‘Siemens oven showing F12, NTC sensor tested or replaced, fault persists — possible PCB or wiring harness issue.’ Do not attempt to open or replace the control board yourself, as it involves working with mains-level electrical components.
⚖️ Repair or replace?
A professional repair for an F12 fault — covering sensor replacement and labour — typically costs £80–£150 in the UK; a PCB replacement pushes that to £150–£300 depending on the model. If your Siemens oven is under 8 years old and was a mid-to-high-range model (£500+), repair is almost always worth it. For ovens over 10 years old with a PCB fault, replacement is likely the more economical choice given ongoing reliability risk.