How to Diagnose an Oven That Won't Heat

Customer says the oven won't heat. Stove top works fine. They've been eating takeout for three days.

This is another call where the diagnosis is clean if you think about it logically. The oven has a heat source (element or burner), a temperature control (thermostat or electronic board), and safety devices in between. Something in that chain isn't working. Your job is to find which link broke.

Electric and gas ovens share the same logic but different components. We'll cover both.

Electric Oven: The Bake Circuit

Check the Bake Element First

The bake element is the oval-shaped heating element on the bottom of the oven cavity. When it works, it glows bright red-orange. When it fails, it either doesn't glow at all or glows unevenly with visible burn-through spots.

Do a visual inspection first. Open the oven, look at the bake element. If you can see a break, a blister, or a spot where the element has burned through the sheath — that's your answer. Replace it.

If it looks fine visually, test it. Unplug the range (or kill the breaker — ranges are on a dedicated 240V circuit). Pull the element forward — it's usually held by two screws at the back wall of the oven cavity. Disconnect the wires from the element terminals. Test resistance: a good bake element typically reads 20-50Ω depending on the wattage. OL means it's open. Also test each terminal to the element sheath (ground test) — should be OL. Any continuity to ground means it's shorted.

Check for Power at the Element

If the element tests good but doesn't heat, it's not getting power. With the range plugged in and the oven set to bake at 350°F, carefully check for voltage at the wire connector where the element plugs in. You should see 240V (or close to it) when the oven is calling for heat.

Safety note: you're testing live 240V. Keep your hands on the insulated portions of your meter leads. Don't touch anything inside the oven cavity with your hands. If you're not comfortable with live voltage testing, unplug the unit and test the circuit for continuity back through the control board instead.

If you have 240V at the connector but the element doesn't heat, the element is bad (even if it passed the resistance test — sometimes they fail under load). If you have 0V when the oven should be calling for heat, the problem is upstream.

Check the Oven Temperature Sensor (Electronic Controls)

Modern ranges with electronic controls use a temperature sensor (thermistor) instead of a mechanical thermostat. The sensor is a thin metal probe, usually mounted at the top-rear of the oven cavity.

The control board reads the sensor's resistance to determine the oven temperature. At room temperature (~70°F), most sensors read approximately 1,080-1,100Ω. This value increases as temperature rises.

Test it: unplug the range, disconnect the sensor from the control board (or at the sensor's plug), and measure resistance. If it reads OL, 0Ω, or a value way outside the expected range, the sensor is bad. This is a common failure — the sensor burns out from years of heat exposure.

If the sensor reads correctly but the oven still won't heat, the control board may not be sending power to the element relay. Check for voltage at the board's output terminal for the bake circuit (the service manual tells you which pins). If no output voltage when the oven is set to bake, the relay on the board has failed. Replace the board.

Check the Oven Thermostat (Mechanical Controls)

Older ranges use a mechanical thermostat with a capillary tube that runs into the oven cavity. The thermostat opens and closes contacts based on the oven temperature.

Test the thermostat contacts for continuity when the thermostat is turned to a temperature setting. If the contacts don't close (no continuity), the thermostat has failed.

Gas Oven: The Ignition System

Gas ovens use either a hot surface igniter (most common in modern ovens) or a spark ignition system. The hot surface igniter is the most frequently replaced part in gas oven repair.

How the Gas Oven Ignition Works

The sequence is similar to a gas dryer:

1. You set the oven to bake. The control board (or thermostat) sends power to the igniter.

2. The igniter heats up over 60-90 seconds, glowing bright orange.

3. As the igniter reaches operating temperature, its resistance drops and current flow increases.

4. When current reaches a threshold (typically 3.2-3.6 amps), the gas safety valve opens.

5. Gas flows to the burner and ignites from the glowing igniter.

If any step fails, no heat.

Check the Igniter (Most Common Gas Oven Failure)

Turn the oven to bake and watch the igniter through the oven floor opening or by looking through the broiler drawer opening at the bottom.

If the igniter doesn't glow at all: It's either burned out or not getting power. Check power at the igniter harness. If voltage is present but no glow, replace the igniter.

If the igniter glows but the gas never lights: The igniter is weak. It glows enough to be visible but doesn't draw enough current to open the safety valve. This is the classic gas oven failure — the igniter works just well enough to look functional but not well enough to actually do its job. Replace it.

You can confirm this with an amp clamp on the igniter circuit wire. If it's drawing less than 3.0 amps after heating for 90 seconds, it's too weak to open the valve. A good igniter draws 3.2-3.6 amps at operating temperature.

If the igniter glows bright and you hear gas flowing but it doesn't ignite: This is rare but dangerous. The igniter might be positioned incorrectly after a previous repair, or the burner orifice could be partially clogged. Shut off the gas immediately if you smell gas without a flame.

Check the Gas Safety Valve

If the igniter is strong (confirmed by amp draw) but the gas valve doesn't open, the valve itself may have failed. Safety valves are bimetal-operated — the igniter's current heats a bimetal strip inside the valve that physically opens the gas port.

Test the valve by measuring resistance across its coil terminals. Compare to the service manual spec. If the coil is open, replace the valve. Gas safety valves are not field-repairable.

Check the Oven Thermostat or Control Board

If neither the igniter nor the valve are getting power, trace back to the control. On mechanical thermostat models, the thermostat contacts may have failed. Test continuity across the thermostat when it's set to a temperature. On electronic control models, the board relay may have failed — check for output voltage from the board during a bake call.

Broil Works But Bake Doesn't (or Vice Versa)

This tells you a lot. If broil works fine but bake doesn't, the gas supply, the control board, and the main electrical connections are all good — only the bake-specific circuit has failed. That narrows it to the bake element (electric), the bake igniter (gas), or the specific relay/output on the control board that drives the bake circuit.

Same logic in reverse — if bake works but broil doesn't, focus only on the broil element or broil igniter.

The Diagnostic Flow

Electric:

1. Visual inspection of bake element → look for breaks or burn-through

2. Test element resistance → 20-50Ω normal, OL = bad

3. Check voltage at element connector during bake call → 240V expected

4. Test temperature sensor → ~1,080Ω at room temp

5. Check control board output → relay failure if no output voltage

Gas:

1. Watch the igniter → does it glow?

2. If glow, does gas light? → weak igniter if no

3. Amp clamp on igniter → 3.2-3.6A expected

4. Check gas safety valve → coil resistance per manual spec

5. Trace power back to thermostat or control board

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