How to Fix / Troubleshooting

Safety first: Disconnect the appliance from the mains power supply before working on the cooker.

Steps to check:

Identify which cavity: Note whether the error appears when using the top oven, grill, or a specific function.
Locate the second sensor: In dual-cavity Rangemaster models, the top oven has its own sensor probe. Access it from inside the cavity (usually the rear wall) and from the rear panel.
Check connections: Follow the sensor wires to the control PCB. Reseat the connector firmly. Look for corrosion or heat damage.
Test sensor: Measure resistance at room temperature. Replace the sensor if it is open, shorted, or significantly out of specification.
Harness inspection: Ensure the harness is not trapped under side panels or by the oven frame. Replace it if the insulation is damaged.
If all checks pass: The secondary oven control PCB or the main display PCB may be faulty. Due to live mains and multi-board wiring, this work should be performed by a qualified technician.

The top oven or secondary cavity fails to heat, and the display shows F4 when that oven is selected.

Possible Causes