Why does my oven cook unevenly?

An oven that browns one side and leaves the other pale is not the same problem as one that runs twenty degrees out, and the two get conflated constantly. Uneven means the heat is not being distributed; wrong means the whole cavity is at the wrong temperature.

Safety

Step by step

1. Map it with the bread test.Cover a shelf with slices of white bread, set the oven to around 200°C, and take them out after four or five minutes. The pattern of browning is a map of your oven, and it usually surprises people.
2. Repeat on each shelf position.Ovens are frequently uneven vertically as well as horizontally. Knowing which shelf is the reliable one is worth more than any adjustment you can make.
3. Separate uneven from inaccurate.If everything browns equally but too fast or too slow, that is calibration and a different problem. If one area browns and another does not, that is distribution — and this guide is about the second.
4. Stop crowding the oven.The commonest cause by a distance. Trays that fill the shelf, or two trays close together, block the airflow that moves heat around. Leave a gap around every tray and at least a few centimetres between shelves.
5. Check nothing is blocking the fan.In a fan oven, a large tray directly in front of the fan outlet at the back stops circulation entirely. Move it forward, or use a smaller tray.
6. Check the fan is actually running.Open the door briefly during preheating and listen, or watch whether the light-driven airflow moves. A failed fan turns a fan oven into a poor conventional one, and the symptom is exactly this.
7. Take the baking tray off the base.A tray or foil on the oven floor blocks the bottom element and reflects heat upwards. It is a common habit for catching spills and it produces uneven results.
8. Check the door seal.Run a hand around the closed door for escaping heat, and look at the rubber seal for gaps, hardening or tears. A leaking seal cools one side of the cavity continuously, which shows as a consistent cool corner.
9. Test the door closure with paper.Close a sheet of paper in the door and pull. If it slides out easily at one point and not others, the seal or the hinge has gone at that point.
10. Consider a failed element.A partly failed grill or bottom element heats unevenly rather than not at all. If one region is consistently cold across every test, that points here — and it is a repair rather than an adjustment.
11. Use a baking stone or a heavy tray to even it out.A pizza stone or thick steel plate on a lower shelf, preheated, stabilises the whole cavity by absorbing and re-radiating heat. It is the most effective single thing you can do to a stubbornly uneven oven.
12. Rotate trays halfway through.Once the structure has set — roughly three-quarters through for cakes, halfway for roasting. It works around the problem rather than fixing it, and it works.
13. Clean it.Heavy carbon deposits on the fan, the elements and the walls change how heat radiates and moves. A proper clean genuinely improves evenness on a neglected oven.

Tips

• Once you have the map, use it. Knowing the back left runs hot is more useful than any repair, and it takes ten minutes to find out.
• Fan ovens should be more even than conventional ones. Persistent unevenness in a fan oven points at the fan or at how it is being loaded.
• Two trays at once will never be as even as one. If it matters, cook in batches.

Common mistakes

• Putting a tray or foil on the oven floor — It blocks the bottom element and reflects heat upwards, which unbalances the whole cavity. Use a tray on the lowest shelf instead.
• Filling the shelf edge to edge — Heat has to move around the food. A tray that fills the shelf stops circulation and produces exactly the uneven browning being complained about.

If it doesn't work

Questions people ask