How to Check a Hot Glue Gun Thermostat With a Multimeter

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How to check a hot glue gun thermostat with a multimeter, unplug the gun, let it cool completely, and use the continuity or resistance setting on the leads of the switch or thermostat part. The sources we opened describe the meter functions and the meaning of OL and beep readings. They do not cover hot glue guns, so the wire layout and any temperature value must come from the gun’s own parts information or the manufacturer.

Quick answer

Unplug the glue gun and let it cool. Do not test a gun that is plugged in.
Use the continuity mode on the thermostat or switch leads. Klein’s MM325 manual says a closed path below its threshold gives an audible signal.
An OL reading on a path that should be closed means an open circuit, according to the Klein manual.
The sources we opened do not give a thermostat resistance or a temperature value for any glue gun. Compare readings with the part’s own data.

Electrical safety first

A hot glue gun runs on mains voltage and heats its barrel and nozzle to a temperature that can burn skin. Klein’s MM325 manual says: “Do not attempt to measure resistance or continuity on a live circuit.” Its manual also says to keep fingers away from the metal probe contacts during measurement. The thermostat is part of the heater circuit, so always unplug the gun before you open it or touch its leads.

Do not open a glue gun that is still warm, and do not reach into the nozzle or barrel. If the gun has a cord with burn marks, a loose plug, or a smell of burning, stop and replace the gun rather than testing it. Breaker panel and service work belong to a licensed electrician. Check the CAT rating of your meter in its manual, and do not use a meter with damaged leads.

What you are checking

A hot glue gun heats through a heating element. A thermostat or a thermal cutoff, if the model has one, opens and closes the heater path to hold a temperature. Some guns have only a switch and no separate thermostat. The Fluke continuity article describes continuity as the presence of a complete path for current flow, and it describes a closed switch as having continuity. That definition is the basis for this check: a working thermostat in its closed state should show continuity, and an open one should not. The multimeter cannot tell you the temperature it holds.

Tools and setup

You need a digital multimeter with continuity and resistance settings and test leads in good condition. The Klein MM325 manual shows the lead setup: the red lead goes in the V jack and the black lead in the COM jack. Use a small screwdriver to reach the thermostat terminals if the gun must be opened, and label each wire before you disconnect it.

Step-by-step: the continuity check

Unplug the gun. Remove the plug from the outlet and wait until the barrel and nozzle are cool to the touch.
Open the housing only if the gun is designed for it. Use the correct screws and keep them organized. Mark the wire positions before you remove any connector.
Find the thermostat leads. Locate the two leads connected to the thermostat or switch. Disconnect one lead so the part is isolated from the heater.
Set the meter. Turn the function selector to continuity. Klein’s manual says the meter sounds an audible signal when resistance is below 100.
Test the part at room temperature. Touch one probe to each lead. A closed thermostat should show continuity, which means the audible signal sounds and the display shows a low value. An open thermostat shows “OL.”
Switch to resistance for a number. If you need a value, use the resistance setting. The Klein manual says to start at the highest range and move to lower ranges for a better resolution.
Check the other leads. Measure from each thermostat lead to the metal body of the gun. The sources we opened do not give a chassis limit for glue guns, so a low reading is a reason to stop and check the parts information.
Reassemble. Reconnect the leads in their original positions and confirm no wire touches the nozzle or the heater.

Reading the results

Meter reading	What the opened source says	What the reading does not tell you
Continuity beep, low value	Klein MM325: resistance below 100 sounds an audible signal and shows a value.	The temperature at which the thermostat opens. Not stated in the sources.
OL on a closed-state thermostat	Klein MM325: an open circuit shows “OL.”	Whether the fault is in the thermostat or the heater. The source does not say.
Zero or very low resistance	Fluke: very low or zero resistance indicates a short circuit.	Whether the short is in the thermostat or the wiring.
Measurable value at room temperature	Fluke: resistance is the opposition to current flow.	Whether the part opens and closes at the right temperature. The sources do not cover this.

What a room-temperature test cannot show

A thermostat changes state with temperature. A room-temperature check shows only whether the contacts close at that temperature. It cannot show whether they open at the right point when the gun heats. The sources we opened do not describe a heated-state test for glue guns, and we do not describe one here. If the gun heats too much, too little, or not at all, the manual or the maker is the right place to look for the correct procedure.

Common mistakes

Testing a plugged-in gun. Klein’s manual says not to measure resistance or continuity on a live circuit.
Leaving the heater connected. A parallel path through the heater can give a false closed reading. Isolate one lead first.
Reading a beep as a temperature test. A beep shows a closed path at room temperature, nothing more.
Ignoring damage. Klein says not to use the meter or leads if they appear damaged, and a damaged gun should be replaced.

How we chose

We chose sources that explain the meter functions and the meaning of continuity and OL readings, and that we could open and read as text on 2026-10-27: Klein Tools’ MM325 manual, which is the manufacturer’s own document, and two Fluke Learn articles. We searched for glue-gun-specific guidance. The results were mostly craft and parts-store pages, which we did not use as sources.

What we could not verify

The thermostat or heater resistance of any hot glue gun. The sources we opened do not give one.
The temperature at which any glue gun thermostat opens or closes.
The wire layout of any particular gun. Check the parts information for your model.
Whether all guns have a separate thermostat. The sources do not say.
The CAT rating of your meter. Check the meter’s listing or manual.

FAQ

Can I test a glue gun thermostat while it is plugged in?

No. Klein’s MM325 manual says not to measure resistance or continuity on a live circuit.

What does a beep mean on this test?

Klein’s manual says resistance below 100 sounds an audible signal. On a thermostat at room temperature, that means the contacts are closed.

What does OL mean?

The Klein manual says OL shows when the circuit is open. On a thermostat that should be closed, OL means an open path.

Can a multimeter tell me the temperature setting?

No. A multimeter measures electrical values, not temperature. The sources we opened do not describe a temperature check for glue guns.

When should I replace the gun instead?

Replace the gun if the cord is damaged, if the housing shows burn marks, or if the heater path reads open and the gun cannot be repaired from its parts information.

Bottom line

Unplug the gun, let it cool, isolate one thermostat lead, and check continuity at room temperature. A beep means a closed path and OL means an open one, according to Klein’s manual. The sources we opened do not cover glue gun temperatures, so a room-temperature check does not prove the gun heats correctly.

Related guides

Sources

Klein Tools, “MM325 Instruction Manual” (manufacturer manual). https://data.kleintools.com/sites/all/product_assets/documents/instructions/klein/MM325%20Instructions_web.pdf (opened 2026-10-27)

Fluke Learn, “What is Continuity?” https://www.fluke.com/en-us/learn/blog/electrical/what-is-continuity (opened 2026-10-27)

Fluke Learn, “What is Resistance?” https://www.fluke.com/en-us/learn/blog/electrical/what-is-resistance (opened 2026-10-27)