Food Burns Underneath but Stays Raw on Top: Why Is My Gas Oven's Heat Uneven?

In most home gas ovens the heat comes from a single burner at the bottom, so it is normal for the lower part to be a little hotter. But if food keeps burning underneath and staying raw on top, the cause is usually: the tray on the lowest shelf, a thermostat that doesn't read the heat accurately, a weak or uneven flame from a blocked burner, a worn door seal letting heat out, or cooking without preheating. Start by moving the shelf and preheating, then test the heat with an oven thermometer. If the gap is large, the thermostat or burner needs checking.

Food burnt underneath and raw on top is one of the complaints we hear most, especially with pastries, cakes and oven rice. Before we look at faults, it helps to know how a gas oven spreads its heat, because sometimes part of the problem is how the oven is used rather than the oven itself.

We start with the causes you can try and fix yourself in minutes, then move on to faults that need checking, and finish with a simple way to test your oven's heat at home so you know whether the oven really is the problem.

How does a gas oven heat up?

A traditional home gas oven has a burner at the bottom, under a metal floor. The flame heats the floor and the air above it, and the hot air rises to the top of the oven and leaves through the vent. So the floor and lower part are hotter from direct radiant heat, and the upper part is hotter from the air. Many ovens also have a separate top grill for browning, and some newer ones have a fan to move the air around.

Causes in how the oven is used

• The tray on the bottom shelf: too close to the heat. The middle shelf suits most recipes.
• No preheating: when the tray goes into a cold oven, the burner runs flat out for a long time to heat the oven, so the base gets far more direct heat than it should.
• A dark or very thin tray: dark trays absorb more heat, and thin ones pass it straight to the base.
• Opening the door a lot: each opening lets hot air out from the top, and the burner makes up for it from below.
• Not using the grill: some dishes need the top grill for the last few minutes to brown.

Causes that need checking

Test your oven's heat yourself

The most accurate way is an oven thermometer, sold cheaply in kitchenware shops. Steps:

1. Put the thermometer in the middle of the middle shelf.
2. Set the oven to 180 degrees.
3. Wait twenty minutes without opening the door.
4. Read the thermometer through the glass, or open the door quickly.
5. Read it again ten minutes later.

A difference of ten to fifteen degrees is normal in most home ovens, because the thermostat cycles within a range. If the gap is clearly bigger than that, or the readings swing a lot, the thermostat needs checking.

A quick test without a thermometer: lay slices of toast bread across the whole middle shelf and run the oven at 180 degrees for ten minutes. The darker slices show you the hot spots in your oven.

The thermostat: the part that controls everything

In a gas oven, the thermostat reads the heat through a metal sensor inside the oven and controls how much gas reaches the burner. If the sensor is dirty, bent or out of place, or the thermostat has weakened with age, it reads the heat wrongly. Then it either keeps the burner on full so food burns, or turns the flame down too early so food stays raw. The technician compares the real temperature with the dial and decides whether adjusting the sensor is enough or the thermostat needs replacing. If it does, he tells you the part type and price before fitting it, as on our gas oven spare parts page.

The door seal: a silent heat leak

The seal is the rubber or fibre edging around the oven opening. Heat and age make it stiffen, crack or come loose, so heat escapes from the top and the burner works harder from below to make up for it. The sign is clear warmth when you hold your hand near the door edges, or grease and soot marks around the front. Replacing it is a quick, simple job.

What the technician checks

• Measuring the oven's real temperature against the dial.
• Checking the burner flame on every side and clearing blocked ports.
• Checking the thermostat sensor and its position.
• Checking the seal, hinges and how the door closes.
• Checking the fan, if there is one.
• A test run after the repair.

All of this is part of our gas oven repair service, with the cost given before work starts. If the flame itself is yellow or weak, also read why your oven flame is yellow.

Tips by dish

If you have set the shelf and preheating as above and every dish still turns out the same, the problem is the oven rather than the method, and that is when it needs checking.

Common questions