How to Fix a Microwave Not Heating

Overview

A microwave that won't heat is often due to a faulty magnetron. This guide covers diagnosing and fixing the issue.

Step-by-Step Fix

1. Before you begin any inspection or repair, always unplug the microwave from the mains socket to prevent electric shock; never assume it's off just because the light isn't on. Once unplugged, carefully remove all screws securing the outer casing, usually located on the back and sides, and then slide or lift the cover off to expose the internal components.
2. With the casing removed, locate the door interlock switches, typically found near the door latch mechanism, and use a multimeter set to continuity mode to test each switch individually. The switch should show continuity when pressed and open when released, indicating it's functioning correctly; replace any switch that fails this test before proceeding, as faulty door switches are a common safety issue.
3. Carefully locate the magnetron, a large metallic component with cooling fins, and disconnect its power wires while remembering that high voltage capacitors can store a lethal charge even after unplugging, so discharge them safely using a screwdriver with an insulated handle across its terminals. Set your multimeter to a low ohms range and check for continuity between the magnetron's terminals and between each terminal and its casing; if there's no continuity or continuity to the casing, the magnetron is faulty and must be replaced.
4. Next, locate the high voltage diode, which is usually a small, black cylindrical component connected to the high voltage capacitor and the chassis. Use your multimeter on the diode test setting to check for continuity in one direction only; if it shows continuity in both directions or neither, the diode is defective and needs replacing, as a faulty diode prevents proper high voltage generation.
5. Once any faulty parts have been replaced and all connections are securely re-established, carefully refit the outer casing, ensuring all screws are tightened properly. Plug the microwave back into the mains and perform a test by heating a cup of water for a short period to confirm it now heats effectively and operates safely.

Common Symptoms & Diagnostic Resolutions

Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.

Frequently Asked Questions