Oven
F21
The F21 error code on an AEG oven indicates a fault with the oven’s temperature sensor (NTC probe) or its associated wiring. It’s a moderately serious fault — your oven will typically stop heating entirely until it’s resolved.
What does this error mean?
F21 means the oven’s control board is receiving an abnormal signal from the NTC temperature sensor — the small probe inside the oven cavity that monitors heat levels. The reading is either out of the expected range, absent altogether, or erratic. Without a reliable temperature signal, the oven’s electronics shut down the heating element as a safety precaution to prevent overheating.
Est. repair cost
£15–£40 DIY (NTC sensor part only); £80–£150 professional repair; up to £250 if PCB replacement is needed
🔍 Likely causes
🛠️ Step-by-step fix
Power off and reset: Switch the oven off at the wall socket or trip the circuit breaker. Wait 10 minutes, then restore power. If F21 clears, it was a temporary glitch — monitor the oven closely for recurrence.
Inspect the sensor probe visually: With the oven cold and unplugged, open the oven door and locate the NTC sensor — it’s usually a small metal rod mounted on the back wall or side of the oven cavity. Check for obvious damage, burning, or a disconnected wire.
Check the sensor connector: Carefully pull the sensor’s wiring plug free (it usually clips on) and reseat it firmly. Corrosion on the pins? Clean gently with electrical contact cleaner spray (available at Screwfix or Toolstation, ~£5).
Test or replace the NTC sensor: AEG oven NTC sensors can be tested with a multimeter — at room temperature (20°C) they typically read around 10,000 ohms (10kΩ). A reading far outside this range confirms a dead sensor. Replacement AEG-compatible NTC probes cost £15–£40 online (try 4ourhouse.co.uk or espares.co.uk) and are a straightforward DIY swap on most models — two screws and a plug connector.
Clean around the sensor: If there’s significant grease or residue caked onto the probe, clean the area with oven cleaner and a cloth, then retest. This alone rarely cures F21 but is worth doing before fitting a new part.
If the sensor tests fine and F21 persists: Stop DIY here. A healthy sensor with a persistent F21 fault points to a wiring harness or PCB issue — both require a qualified appliance engineer to diagnose safely.
📞 When to call a professional
Call an engineer if replacing the NTC sensor does not clear the F21 code, or if you find burnt, melted, or broken wiring in the harness — do not attempt to repair oven wiring yourself. When you call, tell the engineer you have an AEG oven showing error code F21, that you’ve already checked or replaced the NTC sensor, and describe any wiring damage you spotted.
⚖️ Repair or replace?
A professional repair for F21 on an AEG oven — typically a sensor swap or wiring repair — costs £80–£150 including labour and parts. If the fault lies with the PCB, expect £150–£250+. For an oven under 8 years old, repair almost always makes financial sense. If your oven is over 10 years old and the repair quote exceeds £150, a new mid-range AEG or equivalent oven (£400–£700) is often the more cost-effective long-term choice.