The short answer
This page covers a Frigidaire microwave that runs a full cycle and produces no heat at all: the light is on, the turntable moves, the timer counts down, and the food is cold. Rule out the door interlocks, a demo mode and the supply, and then stop. A total heat loss points at high-voltage components that must never be touched by an owner. Weak or uneven heating is a different fault and the companion page covers it.
Causes, ranked for this Frigidaire microwave
- Demo or showroom mode enabled — Why: These modes run every visible function with the heating disabled, which produces this exact complaint, and they are cleared from the control panel for nothing.
- A door interlock not confirming — Why: The interlock chain must agree before the magnetron is energised, so a marginal switch lets the oven run its cycle while withholding heat entirely.
- High-voltage diode, capacitor or transformer failed — Why: These are the classic total-heat-loss failures, and they are also the components that store and carry lethal energy, which is why owner work ends at the diagnosis.
- Magnetron failed — Why: A magnetron at end of life gives no heat with everything else working, and it is confirmed only with instruments after the rest of the circuit is proven.
- Supply voltage too low at the socket — Why: A microwave on an overloaded or shared circuit can run its controls and still not sustain the magnetron, which is worth eliminating because it is not an appliance fault at all.
What to check, in order
- check the display for a demo or showroom indication and clear it. — Because: it produces this exact symptom for free and it is the only cause an owner can fix.
- run the standard heating test with a cup of water rather than judging by a plate of food. — Because: it separates no heat from weak heat, which are different faults.
- confirm the oven is on its own socket with no extension lead. — Because: a starved supply runs the controls and not the magnetron.
- note any loud hum or a breaker trip at the moment the cycle starts. — Because: either one means stop using the oven rather than continue testing.
Checks you can safely do yourself
- Check the control panel and manual for a demo or showroom mode indication, and clear it if present. — Tools: the owner manual — Time: several minutes
- Put a cup of cold water in the oven, run it briefly at full power and check whether the water is warm at all. — Tools: a microwave-safe cup — Time: several minutes
- Plug the oven directly into its own socket, removing any extension lead or shared adapter, and repeat the water test. — Tools: none — Time: several minutes
- Listen during the cycle for an unusually loud hum or buzz and note whether the breaker holds. — Tools: none — Time: several minutes
- If the water stays cold, unplug the oven and arrange service. Stop here: nothing inside the cabinet may be opened, tested or discharged by an owner. — Tools: none — Time: a minute
Before you open anything
Safety
unplug-before-service branch-circuit-15-20a
Never remove the outer cabinet of a microwave. The high-voltage capacitor stores a lethal charge long after the oven is unplugged and does not discharge on its own reliably. Never run the oven empty, and stop using it entirely if it hums loudly, trips a breaker, smells of burning, or arcs inside.
Where the owner fix ends
Clearing a demo mode, running the water test and correcting the supply are owner work; nothing else here is. Call a technician the moment the water test confirms no heat on a properly supplied oven, because the diode, capacitor, transformer and magnetron all carry or store lethal energy and are tested only with the right instruments.
Nearest pages of the same kind
Generalized information — what this page does not cover
family model
This page is generalized information covering only the total heat loss branch of the Frigidaire microwave heating complaint; the companion page linked below covers weak and uneven heating. Neither separates countertop, over-the-range and built-in formats. No family-level or model-level page exists in this reference yet; when one is published it will be linked here.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
