Multimeter Says OL? Your Radiant Heater Glow Bar May Be Bad

Introduction

A radiant heater that will not ignite can sometimes come down to one small part: the hot surface igniter, commonly called a glow bar. Fortunately, diagnosing it is straightforward. All you need is a multimeter set to resistance, or ohms.

An OL reading is often the first big clue. It usually means the igniter circuit is open, which points to a broken glow bar that needs replacement.

 

What You Need to Diagnose a Hot Surface Igniter

The only test tool required is a multimeter capable of measuring resistance. Set the meter to the ohms setting before beginning the test.

To reach the igniter, remove the heater access panel. Inside, locate the hot surface igniter and its wire harness. Disconnect the harness so you can test the glow bar itself rather than reading through the rest of the heater wiring.

 

How to Test the Glow Bar With a Multimeter

Once the harness is disconnected, place one multimeter probe on each of the two prongs inside the glow bar connector. This checks the resistance through the igniter element.

Caption: Test directly across the two glow bar terminals with the harness disconnected.

 

The reading tells you whether the hot surface igniter is intact:

• OL or overload: The circuit is open. The glow bar is most likely broken and should be replaced.
• An unstable reading: Resistance that jumps between OL and very high values, including thousands of ohms, can indicate a developing failure.
• A stable reading between 50 and 150 ohms: The glow bar is in the expected operating range.

In the example shown here, the failed igniter reads OL. That is consistent with a break in the element.

 

Why an Inconsistent Ohms Reading Matters

Not every bad glow bar fails in one clean break. A silicon carbide igniter can develop a small hairline crack that creates intermittent resistance readings. The meter may alternate between overload and extremely high resistance instead of holding a stable value.

Look closely at the ashy silicon carbide section of the igniter. A crack beginning in this area is a warning sign that the glow bar is on its way out, even if it has not completely failed yet.

 

Replacing a Bad Radiant Heater Glow Bar

If the meter reading confirms a failed igniter, replacement is simple:

1. Remove the retaining spring from the existing glow bar.
2. Slowly pull the old igniter out of the tube.
3. Inspect it for a visible break or crack in the silicon carbide element.
4. Gently insert the new hot surface igniter into the tube.
5. Slide the attachment spring back over the igniter to secure it.

Handle the replacement igniter carefully during installation. The silicon carbide portion is the working element, and it should be seated properly in the tube before the retaining spring is installed.

 

Confirm the New Igniter Before Reassembly

Before closing up the heater, test the new glow bar the same way: probe the two connector terminals with the multimeter set to ohms.

A good hot surface igniter should measure between 50 and 150 ohms. The replacement tested here measures approximately 77 ohms, which is right where it should be.

Caption: A stable resistance reading in the 50 to 150 ohm range confirms a good glow bar.

 

Finish the Repair

Reconnect the harness, tuck the wiring back into place, and reinstall the access cover. At that point, the glow bar has been diagnosed and replaced.

When a radiant heater glow bar reads OL, do not ignore it. A quick resistance test can identify a broken igniter, catch a cracking element before it fails completely, and help get the heater back to reliable operation.

 

Need Help Troubleshooting a Radiant Heater Ignition Issue?

If your radiant heater is not igniting, the hot surface igniter, or glow bar, is one of the first components worth checking.

At Great Lakes Radiant, we help walk through real-world radiant heater troubleshooting every day. From testing glow bar resistance and identifying OL readings to reviewing ignition sequence, wiring, burner operation, gas pressure, controls, and replacement parts, we’ll help you narrow down the issue and avoid unnecessary guesswork.

Whether you’re diagnosing a heater that will not light, confirming whether a glow bar has failed, or double-checking your multimeter readings before replacing a part, we’ll help you get it right the first time.

Send us photos, heater model information, resistance readings, symptoms, or fill out our Project Details form, we’re here to help.

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