HOW-TO GUIDE
How to Test a Thermal Fuse With a Multimeter
By the OhmSavvy Research Team ·
Unplug the appliance first
Thermal fuse vs thermostat and thermal cutoff
Appliances often carry several temperature-protection parts in the same circuit, and they behave differently on a meter. Knowing which one you have stops you condemning a part that is simply doing its job.
Thermal fuse (one-shot)
Closed until it reaches its rated temperature, then open forever. Must be replaced.
Auto-reset thermostat
A bimetal disc that opens when hot and closes again as it cools. Reads closed at room temperature.
Manual-reset cutoff
Opens when overheated and stays open until you press its reset button.
Cycling thermostat
Switches the heater on and off in normal use to hold the working temperature.
1Locate and isolate the fuse
In dryers the thermal fuse is usually on the blower housing or the heater duct, behind the rear or lower front panel; in coffee makers and kettles it is typically clipped against the heating plate under the base. The service manual or wiring diagram, often taped inside the cabinet, shows the location. Photograph the wiring, then pull one wire off the fuse so the meter only sees the fuse.
2Measure resistance across it
Set the meter to continuity or the lowest ohms range and touch one probe to each terminal. Polarity doesn't matter. A good thermal fuse reads essentially the same as the shorted test leads, a fraction of an ohm. A blown fuse reads OL. There is rarely anything in between: a fuse showing a high but finite value should be treated as faulty.
3Check the thermostats too
Test the high-limit and cycling thermostats the same way at room temperature: each should read closed. A thermostat that reads open while cold has failed. One that reads closed is not proven good, because the classic failure is a cycling thermostat that sticks closed and never opens, letting the temperature climb until the fuse blows.
Reading the results
| Part | Reading at room temperature | Meaning |
|---|---|---|
| Thermal fuse | Near 0 Ω | Intact; look elsewhere for the fault |
| Thermal fuse | OL | Blown; replace it and find the cause |
| Auto-reset thermostat | Near 0 Ω | Closed as expected (may still stick closed when hot) |
| Auto-reset thermostat | OL when fully cool | Failed open; replace |
| Manual-reset cutoff | OL | Tripped; press reset and retest, then find why it tripped |
A blown thermal fuse is a symptom, never the fault
If you're new to reading an open circuit, our guide to what OL means explains why that reading confirms a blown fuse rather than a meter problem.
Meters for appliance fuse checks
The fuse test itself is an unpowered continuity check, but the same meter usually ends up confirming the outlet, the cord and the heating element afterwards. A backlit display helps inside a dark dryer cabinet, and a CAT rating matters once you move on to live checks at the outlet.
Meters for dryer and appliance repair
True RMS, CAT III 600V, 6,000-count backlit display, plus capacitance for motor start capacitors. Hands-on Tested.
Adds NCV and a LoZ mode to the 115's feature set, useful for confirming an appliance circuit is dead. Hands-on Tested.
Budget True RMS with auto-ranging, NCV and a backlight. CAT II 600V, so keep it to appliance and outlet work.
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Frequently asked questions
Can a thermal fuse be reset?
No. A true thermal fuse is a one-shot device: once it reaches its rated temperature, an internal pellet or alloy melts and the circuit stays open permanently. Parts that close again on their own when they cool, or that have a reset button, are thermostats or thermal cutoffs, which are a different component even though they may look similar.
What temperature rating should a replacement thermal fuse have?
Exactly the same as the original, which is printed on the body or listed in the appliance's parts list, along with the same current and voltage rating. A higher-temperature fuse can let the appliance get hot enough to damage parts or start a fire before it acts. For appliances, use the manufacturer's replacement part where one exists.
Why does my dryer thermal fuse keep blowing?
The most common cause is restricted airflow: a lint-clogged exhaust vent, a crushed duct, or a blocked lint screen housing, which lets heat build up in the drum. A cycling thermostat stuck closed or a heating element shorting to the cabinet can also do it. Clear and check the full vent run and test the thermostats before fitting another fuse.
Can I test a thermal fuse without removing it?
Often you can, if the appliance is unplugged and you pull one wire off the fuse's terminals so nothing else is measured in parallel. With both wires attached, the meter can read through other parts of the circuit and show a misleading value. Removing one connector is quicker than removing the whole fuse and just as reliable.
Can I solder a new thermal fuse in place?
Be careful. The heat from soldering close to the body can trip a new thermal fuse before it's ever used. Crimp connections are the usual method for appliance fuses; if you must solder, keep the joint well away from the body, heat-sink the lead between the joint and the fuse, and work quickly. Test it again with the meter after fitting.
