How to Test a Screed Heater That Isn’t Producing Heat
When a screed heater stops working, it can bring your operation to a halt. Whether you’re working with asphalt equipment or industrial heating systems, identifying the issue quickly can save time, money, and frustration.
The good news? In most cases, you can diagnose a screed heater with a few simple tools and a systematic approach. Below is a practical guide to help you determine whether the problem is the heater itself or something else in the system.
Start with Safety
Before performing any tests, make sure the unit is completely powered down. Disconnect all power sources and allow the heater to cool. Always verify with a meter that no voltage is present before touching wires or terminals.
Verify the Power Supply
Before assuming the heater has failed, check whether it’s actually receiving power.
Use a multimeter to measure voltage at the heater terminals and compare it to the unit’s rated voltage (commonly 120V or 240V). If there’s no voltage present, the issue is likely upstream—such as a breaker, relay, wiring issue, or controller.
Many “bad heater” calls turn out to be power supply problems.
Perform a Visual Inspection
Next, take a close look at the heater and its connections. Physical damage can often point you directly to the issue.
Look for:
- Burn marks or discoloration
- Loose or broken wires
- Damaged insulation
- Cracks in the heater sheath
If you see any of these signs, the heater has likely failed and should be replaced.
Test the Heater’s Resistance
The most reliable way to check a screed heater is by measuring its resistance.
Disconnect the heater leads and set your multimeter to measure ohms (Ω). Place the probes across the heater terminals.
A functioning heater will show a stable resistance value. If your meter reads “OL” or infinite resistance, the element is open—meaning it has burned out. If the reading is extremely low, the heater may be shorted.
You can also calculate what the resistance should be using the formula:
R = V² ÷ W
For example, a 240V, 1000W heater should measure around 57.6 ohms. If your reading is significantly different, the heater is likely defective.
Check for Ground Faults
Another important test is checking whether the heater is shorting to ground.
With your multimeter set to continuity or high resistance, measure between each terminal and the heater’s metal sheath. There should be no continuity. If there is, the heater has a ground fault and must be replaced.
Don’t Overlook the Controls
If the heater passes all tests but still isn’t heating, the issue is likely elsewhere in the system.
Common culprits include:
- Faulty temperature controllers or thermostats
- Failed solid-state relays (SSR)
- Damaged wiring harnesses
- Bad RTD or thermocouple sensors
In many cases, the heater itself is fine—the control system is what’s preventing it from turning on.
Common Causes of Screed Heater Failure
Based on real-world troubleshooting, the most frequent issues include:
- Burned-out heating elements
- Loose or corroded electrical connections
- Failed relays or contactors
- Broken lead wires near the cold section
- Sensor failures preventing activation
Final Thoughts
Testing a screed heater doesn’t require specialized equipment—just a multimeter and a logical process. By checking power, inspecting the heater, and measuring resistance, you can quickly determine whether the heater needs replacement or if the issue lies elsewhere.
Taking the time to diagnose the problem correctly can prevent unnecessary replacements and reduce downtime.
If you’re troubleshooting a specific heater and aren’t sure what your readings mean, feel free to reach out or share your measurements. A quick review can often confirm whether your heater is still good or ready to be replaced.