Straight to it
F3T4 means the reading arriving from the magnetron temperature thermistor and its wiring fell outside the band the control is built to trust. Before anything is replaced, a connector at the sensor that has worked loose with heat cycling accounts for a large share of these, and it is free to eliminate.
The code table for this reading
Reference| Code | Documented meaning |
|---|---|
| F3T4 | There may be a problem with the Magnetron Temperature Thermistor or the associated wiring. |
What an owner observes
- The code appears and the cycle stops heating — Everything else looks normal — lights, fan, display — and only the heat is missing.
- The fault comes and goes with temperature — An intermittent connection opens as the metal expands and closes again when it cools, which is why the code often arrives part-way through a long cycle.
- NEAR MISS - nothing heats and no code shows at all — That is a power or element fault rather than a reading fault, and it belongs on the page for that symptom.
The ranked causes behind this reading
- A loose or corroded connector at the thermistor — Ranked first because it is the failure that needs no part: the probe is fine, the joint carrying its signal is not, and heat cycling at the back of the cavity is what works a pin loose.
- Magnetron temperature thermistor out of tolerance — Second: the element itself drifts or opens with age, and once it reads outside the accepted band the control has nothing to work from.
Check these in this order, and why
- Power the machine down fully and see whether the code returns — Costs nothing and separates a latched one-off read from a live fault.
- Follow the harness for rub marks where it crosses metal — A witness mark tells you the fault is in the wire, not in the part at either end.
Steps you can take yourself
- Clear the code with a full power-down — Switch the breaker off, let the control lose its stored state, then switch it back on and start a short cycle.
About 5 min
- Run the shortest cycle the appliance offers and watch for the code — A short cycle that stays clean while a long one fails tells a technician the fault is thermal.
About 20 min
- STOP HERE if the next step is a meter across the probe terminals — That means a panel off and a connector back-probed, which is where an owner check ends and a service call begins.
Where the risk actually is
Safety
The hazard here is specific and it is not the mains. A microwave power supply stores a lethal charge in its capacitor after the appliance is unplugged; it does not bleed away on its own in any useful time. Unplug the appliance or switch off its breaker before any panel comes off, and treat the cabinet itself as closed to owners.
The point at which you call
The line is straightforward. Call once the code survives a full power-down: a repeatable reading fault is a probe, a harness or a board, and telling those three apart needs a meter and the resistance table for that model line.
Codes next to this one
What this page does not cover
Scope, stated plainly: the model lines that use this probe on this cavity, and this code only. Model-specific detail - the pinouts, the resistance values, the part numbers - is not on this page, because those differ between families and a wrong figure here would be worse than no figure. The index linked below lists the pages for specific families and models where they exist, and a page about your model outranks this one.
The full code index for this appliance
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
