A maintenance technician pulled a 3 kW PTFE immersion heater from a plating tank after the tank stopped heating. The controller was calling for heat, the breaker was closed, and voltage was present at the heater terminals. Yet no current was flowing. The technician suspected an element break but did not know which tests would confirm it. Replacing the heater without testing would risk installing a new unit into a circuit that had a different problem.
A broken resistance element is one of the few PTFE immersion heater faults that can be confirmed with basic electrical instruments. The tests are simple, but they must be performed in the correct sequence to avoid misleading results. A multimeter, a clamp meter, and a megohmmeter together provide a complete picture of the heater's electrical condition.
Test 1: Continuity and Resistance Measurement
The first test is a resistance measurement across the element terminals. Disconnect the heater from the supply. Set the multimeter to the lowest resistance range-typically 200 Ω or auto-range. Place the probes across the two element terminals.
A healthy element reads a resistance close to the nameplate value. For a 3 kW, 240V heater, the expected resistance is approximately 19.2 Ω. A reading within ±5% of that value indicates the element is intact. An infinite reading-displayed as OL or 1-indicates an open circuit, confirming an element break.
A reading significantly lower than nameplate indicates a short between turns or a partial break that has created a low-resistance path. Either condition requires replacement.
| Heater Wattage | Voltage | Expected Resistance | Acceptable Range | Open Circuit Reading |
|---|---|---|---|---|
| 2 kW | 240V | 28.8 Ω | 27.4–30.2 Ω | OL / infinite |
| 3 kW | 240V | 19.2 Ω | 18.2–20.2 Ω | OL / infinite |
| 4 kW | 240V | 14.4 Ω | 13.7–15.1 Ω | OL / infinite |
| 5 kW | 240V | 11.5 Ω | 10.9–12.1 Ω | OL / infinite |
| 6 kW | 240V | 9.6 Ω | 9.1–10.1 Ω | OL / infinite |
Expected resistance values for common PTFE immersion heater ratings at 240V
Test 2: Insulation Resistance to Ground
The second test checks the insulation between the element and the sheath. Set the megohmmeter to 500V DC. Connect one lead to either element terminal and the other lead to a known ground-the flange or a bare metal part of the sheath.
A healthy heater reads above 100 MΩ. A reading between 10 and 100 MΩ indicates moisture or contamination in the MgO insulation. A reading below 10 MΩ indicates significant insulation degradation and a high risk of ground fault. A reading near zero indicates a direct short between the element and the sheath.
This test distinguishes an element break from an insulation failure. A heater with an open element and good insulation has a broken resistance wire. A heater with a continuous element and poor insulation has a moisture or contamination problem.
| Insulation Resistance | Condition | Element Status | Recommended Action |
|---|---|---|---|
| >100 MΩ | Healthy | Intact | Return to service |
| 10–100 MΩ | Moisture present | Intact | Dry out, monitor |
| 1–10 MΩ | Significant moisture | Intact or broken | Replace heater |
| <1 MΩ | Insulation failure | Intact or broken | Remove from service |
| 0 Ω | Direct short | Broken or shorted | Remove from service |
Insulation resistance interpretation for PTFE immersion heaters
Test 3: Voltage and Current Under Load
If the resistance and insulation tests are normal but the heater still does not heat, the problem may be in the supply circuit rather than the heater. Reconnect the heater and energize the circuit. Measure the voltage at the heater terminals with the controller calling for heat.
A voltage reading close to the nameplate value indicates the supply is reaching the heater. A reading significantly lower-or zero-indicates a problem in the supply circuit: an open breaker, a failed contactor, a blown fuse, or a wiring fault.
Measure the current with a clamp meter around one supply conductor. A current reading close to the expected value confirms the heater is drawing power. A zero reading with voltage present confirms an open element or a broken connection inside the heater. A current reading lower than expected indicates reduced voltage or increased resistance.
| Voltage Reading | Current Reading | Diagnosis | Next Step |
|---|---|---|---|
| Normal | Normal | Heater operating | Check process conditions |
| Normal | Zero | Open element or internal break | Replace heater |
| Normal | Low | Partial break or high resistance | Replace heater |
| Low | Low | Supply voltage problem | Check supply circuit |
| Zero | Zero | No power to heater | Check breaker, contactor |
Voltage and current interpretation for PTFE immersion heaters under load
Test 4: Terminal-to-Terminal Voltage Drop
A voltage drop test can identify loose or corroded connections that are reducing power to the heater. With the heater energized, measure the voltage between the supply conductor and the heater terminal at each connection point. A voltage drop of more than 2% at any connection indicates a problem.
Loose terminals, corroded lugs, and pitted contactor contacts all add resistance to the circuit. The heater receives less voltage than the supply provides, and its power output drops. The heater is not broken, but it cannot deliver full output.
When the Tests Confirm an Element Break
An open element cannot be repaired. The heater must be replaced. Before installing the replacement, verify that the supply voltage, breaker size, and wiring are correct. A heater that failed prematurely may have been operating at the wrong voltage or with a loose connection that caused overheating.
If the replacement heater also fails within a short period, the cause is likely in the supply circuit or the operating conditions. High voltage, loose connections, or excessive cycling can cause element failure. A voltage check and a review of the operating cycle will identify the problem.
When Testing Reveals a Different Fault
Not every heater that fails to heat has a broken element. The multimeter tests may show a healthy element and good insulation, but the heater still does not operate. In that case, the problem is in the controller, the contactor, the breaker, or the wiring. Testing the heater alone is not enough-the entire circuit must be checked.
When Element Breaks Indicate a Specification Problem
Repeated element breaks in the same tank indicate that the heater is operating outside its design parameters. High voltage, excessive cycling, or vibration can cause element failure. A custom PTFE immersion heater configuration with a higher-resistance element, a lower watt density, or improved vibration resistance addresses the root cause of element failure. The specification process requires the supply voltage, breaker size, duty cycle, and the failure history of previous heaters.
