HOW-TO GUIDE
How to Test a Soldering Iron
By the OhmSavvy Research Team ·
Always test continuity unplugged
Why test before you rely on it
A quick test catches problems before they cost you a ruined joint or a damaged board — particularly worth doing on a secondhand iron, one that's been in storage a long time, or one you suspect has started failing. The four checks below go from safest and simplest (fully unplugged) to most informative (actually soldering with it).
01
Cold continuity
Unplugged, multimeter on the element
02
Visual check
Cord, plug, tip condition
03
Timed heat-up
Plugged in, watch how fast it heats
04
Solder-melt test
Confirm it actually solders well
1Cold continuity check (always unplugged)
With the iron fully unplugged, set a multimeter to resistance (ohms) mode and touch the probes across the heating element's terminals (on a two-part station, this is usually accessible at the handpiece connector; on a simple iron, check the manufacturer's documentation for where the element terminals are exposed, if at all). A stable, finite reading means the element has continuity; an infinite or "OL" reading points at an open, failed element; a reading at or very near zero ohms suggests a short.
What resistance should you actually expect?
There's a real reason the "right" number varies so much between irons: a resistive heating element's resistance follows R = V² ÷ P, so it depends on both the iron's wattage and the mains voltage it's designed for. A higher-wattage element has lower resistance at the same voltage, and the same wattage element rated for 230V mains reads roughly four times the resistance of one rated for 120V, since resistance scales with the square of the voltage.
Figures above are illustrative, calculated from R = V² ÷ P at 230V — a 120V iron of the same wattage reads roughly a quarter of these values. Always check your specific iron's own documentation rather than relying on a generic figure.
For a US iron the arithmetic is the same with 120V: a 60W element works out to 120² ÷ 60 = 240Ω and an 80W element to 120² ÷ 80 = 180Ω. Treat these as ballpark checks, because many elements read noticeably lower when cold than at operating temperature, and low-voltage station handpieces run from a transformer at a few tens of volts, so their elements typically read only a few ohms to a few tens of ohms. Stations with a separate sensor also have a second pair of contacts at the connector; that sensor reading is a different number from the heater, so check the service manual's pinout before you decide anything has failed.
2Visual inspection of cord, plug, and tip
Check the power cord along its full length for cracks, fraying, or exposed conductor, especially near the plug and near where the cord enters the iron's handle — flex points that see repeated bending. Check the plug for scorch marks or bent/loose prongs. Inspect the tip for the signs of genuine wear covered in our tip care guide — a worn tip can make a perfectly healthy iron seem faulty.
3Timed heat-up test
Plug the iron in (away from anything flammable, on its stand) and time how long it takes to reach a usable soldering temperature, whether that's shown on a digital display or judged by how readily it melts solder. Compare this against the manufacturer's stated figures, or against the iron's own past performance if you've used it before. A healthy element heats at a consistent, predictable rate every time.
4Solder-melt test
Once heated, touch a small amount of solder to the tip. It should melt within a second or two and flow smoothly across a clean tip. Slow, reluctant melting on a known-clean, freshly-tinned tip — ruling out the common causes in our troubleshooting guide — points toward a genuine heat-output problem rather than tip condition or temperature setting.
5Check tip temperature and grounding
For a temperature-controlled station, a tip thermometer tells you whether the display can be trusted. Set a round value such as 350°C, let it settle for a minute and measure with a thermocouple tip tester. A difference within about 10–15°C is generally workable for hobby use; a larger gap suggests a worn tip, a failing sensor or a calibration offset you can correct if the station allows it.
On an ESD-safe station, also check the path from tip to ground. With the station unplugged, measure resistance from the tip to the plug's ground pin, or to the station's ground jack. A reading of a few ohms or less is typical, and many maker manuals call for under about 2Ω. An open reading means the tip is floating and can carry static or leakage to sensitive parts.
Interpreting the results together
| Result pattern | Likely meaning |
|---|---|
| Good continuity, heats normally, melts solder fine | Iron is healthy — safe to rely on |
| Infinite resistance (open), doesn't heat at all | Heating element has failed — needs repair or replacement |
| Good continuity, but heats very slowly compared to before | Element may be degrading, or check for a power/voltage supply issue |
| Heats fine, but solder won't melt or wet properly | Likely a tip condition or temperature-setting issue, not the element — see the not-melting guide |
When to stop and not use the iron
If it fails: replacement irons
An open element or a damaged cord on a cheap plug-in iron usually isn't worth repairing. On a station, replacement heaters and handpieces are often sold separately, so check spares before replacing the whole unit. If you do replace it, these picks from our reviews have readable temperature settings, which makes every test on this page easier to repeat.
Stations with temperature you can verify
Digital readout, ±1°C idle stability per Hakko, and a parameter lock so a calibration offset can't be changed by accident.
85W ESD-safe station (70W iron); Weller quotes about 28 seconds from 50 to 350°C, a useful baseline for the timed heat-up test.
Budget PID station, 90–480°C, with digital calibration and a sleep timer of 5, 10 or 30 minutes.
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Frequently asked questions
Is it safe to test continuity on a soldering iron with a multimeter?
Yes, as long as the iron is fully unplugged from the wall first. You're measuring resistance through the heating element with the multimeter's own small test current, not mains voltage, so there's no shock risk done this way — never test continuity on a live, plugged-in iron.
What resistance reading should a healthy heating element show?
It varies by iron and wattage, so there's no single universal number — what matters is that you get a stable, finite resistance reading (typically tens to a few hundred ohms depending on the model) rather than infinite resistance (open circuit, meaning a broken element) or a reading near zero ohms (a short).
My iron heats up but the multimeter showed infinite resistance when unplugged — what does that mean?
That combination suggests the problem isn't the heating element itself, but something else entirely — recheck your multimeter leads and settings (make sure it's set to resistance/continuity mode, not voltage), since a genuinely open heating element wouldn't heat up at all.
How long should a healthy iron take to reach working temperature?
It depends heavily on wattage and element type — see our ceramic vs. nichrome heating element comparison — but as a rough guide, many common 60-80W irons reach a usable temperature within 30-60 seconds from cold. A dramatic, sudden slowdown compared to an iron's own past performance is more telling than any single absolute number.
How can I check if my soldering iron is actually reaching the temperature it shows?
Use a dedicated tip thermometer with a thermocouple sensor designed for soldering tips, wet the sensor with a little solder and hold the tip on it until the reading settles. An infrared thermometer won't work well, because shiny tinned tips reflect rather than emit infrared. If the reading is well off and your station supports calibration, enter the offset using the maker's procedure.
