Main oven will not heat, display shows F1 shortly after a cooking program is selected.

Safety first: Disconnect the cooker from the mains supply by switching off at the cooker switch and isolating at the consumer unit (breaker) before removing any panels. Allow the oven to cool completely.

Step-by-step checks:

• 1. Power reset: Turn off power for 5–10 minutes, then restore. Re-select a cooking function. If F1 returns immediately, continue below.
• 2. Access the temperature sensor: Open the main oven door and locate the temperature probe (usually a thin metal rod at the rear or side wall). Remove the fixing screws and gently pull the sensor into the cavity to access the connector.
• 3. Check wiring and connector: Inspect the sensor lead for burns, cuts, or crushed insulation where it passes through the rear panel. Ensure the plug is firmly seated and not corroded.
• 4. Test the sensor with a multimeter: With the sensor unplugged, measure resistance across the two terminals. A typical Rangemaster NTC sensor will read roughly 1–1.2 kΩ at room temperature (exact value varies by model). If it reads open (OL) or near 0 Ω, the sensor is faulty.
• 5. Inspect at the control board: Remove the rear or top panel (depending on model) to access the electronic oven control (EOC). Confirm the sensor harness is firmly connected and not heat-damaged.
• 6. Replace if defective: If resistance is out of spec or intermittent when you gently flex the cable, replace the temperature sensor with a Rangemaster-compatible NTC probe. Route the new cable away from hot surfaces and sharp edges.

When to call a professional: If the sensor tests good but F1 persists, the fault may be on the control board sensor circuit, which typically requires board-level replacement and should be handled by a qualified technician.