How to Troubleshoot and Replace Faulty Commercial Dishwasher Heating Coils

How to Troubleshoot and Replace Faulty Commercial Dishwasher Heating Coils

Commercial dishwashers are essential in maintaining hygiene and efficiency in food service operations. One of the most crucial components of these machines is the heating coil, which ensures that water reaches the required temperatures for sanitization and proper cleaning. When a heating coil fails, the dishwasher may deliver cold washes, incomplete cycles, or even shut down entirely, impacting service and compliance with health standards. Recognizing the early signs of dishwasher heating coil failure and understanding how to address them can prevent costly downtime. This guide provides a detailed walkthrough on how to troubleshoot and replace faulty heating coils in commercial dishwashers. Whether you're a maintenance technician, a facility manager, or a restaurant owner, these steps will help restore your equipment’s functionality efficiently and safely.

Common Troubleshooting Steps for Faulty Heating Coils 

Heating coil issues in commercial dishwashers can stem from electrical problems, limescale buildup, internal shorts, or general wear and tear. Here are step-by-step troubleshooting methods for dishwasher heating coil

Safety First

Before starting any work, disconnect the dishwasher from power and water supplies. Ensure the unit is cool to the touch to prevent burns. Put on proper PPE (Personal Protective Equipment) such as gloves and safety goggles. Many dishwashers are hardwired, so you may need to shut off the breaker at the panel.

Review the Error Codes

Modern commercial dishwashers often display error codes when components fail. Refer to the manufacturer’s manual to interpret any codes showing on the control panel. Codes related to heating failure may include symbols or abbreviations like “HE” (heating error) or “TEMP” (temperature failure).

Visual Inspection

Open the access panel to examine the heating coil. Look for signs of:

• Burn marks or discoloration on the element.

• Cracks or breaks in the coil.

• Corrosion or limescale deposits, which can impair heat transfer.

Check for Scale Build-up

Hard water can cause scale to accumulate on the heating element, reducing its efficiency or leading to burnout. Remove the element and examine it for white, chalky deposits. If buildup is present, this may be the root cause of the issue.

Test Electrical Continuity

Using a multimeter set to the Ohms (Ω) setting, test the heating coil for continuity:

• Remove the terminals connected to the heating coil.

• Touch the probes of the multimeter to each terminal.

Verify Voltage Supply

Still using the multimeter, switch to the AC voltage setting. Turn the dishwasher on (if safe and accessible) and measure the voltage across the coil terminals:

• If voltage is present but the coil doesn’t heat, the coil is faulty.

• If no voltage is present, the issue might be with the thermostat, relay, control board, or wiring.

Test the Thermostat and High-Limit Switch

Faulty thermostats or safety switches can prevent the coil from energizing even if it’s functional:

• Check continuity across these components.

• If the thermostat doesn’t close at the set temperature or the high-limit switch is stuck open, they may need replacing.

Inspect the Control Board and Relays

Some dishwashers use relays to control the power to the heating element. If the control board isn’t sending power due to a failed relay or logic error, the coil won’t activate.

Assess Water Temperature

If your dishwasher uses an external booster heater, confirm whether the problem lies there instead of the internal coil. Use a thermometer to test the water temperature:

• Ideal rinse temperature: 180°F (82°C)

• Wash temperature: 150–160°F (65–71°C)

Check Wiring and Connectors

Loose or damaged wiring can lead to intermittent heating failures. Check:

• Terminals for corrosion or looseness

• Wire insulation for heat damage

• Connectors for proper fit

• Resecure or replace any faulty wires.

Test the Unit in Service Mode

Some commercial models feature a diagnostic or service mode. Activate it according to your user manual to check each function independently, including coil activation.

Inspect for Ground Faults

A dishwasher heating coil shorting to the dishwasher’s chassis can cause tripped breakers or erratic behavior. Use a multimeter to check for continuity between each coil terminal and ground. Any reading indicates a ground fault, requiring coil replacement.

Check the Heating Time

If the coil heats but takes too long, it may not be reaching full power. This could be caused by:

• Undervoltage at the terminals

• Partially scaled element

• Intermittent relay faults

• Compare warm-up time with manufacturer specifications.

Test for Resistance Drift

Over time, heating elements can experience increased resistance, leading to reduced heating efficiency. Measure the coil's resistance and compare it to the rated value. A reading significantly higher than spec suggests the element is degrading.

Evaluate Internal Fuses or Thermal Cutoffs

Some heating circuits include hidden thermal fuses or cutoffs to protect against overheating. If these components trip or fail, the coil will not energize:

• Locate these components (they may be near or on the heating element).

• Test them for continuity. A blown fuse or open cutoff will need replacement.

Assess Dishwasher Load and Usage Patterns

Frequent overloading or poor maintenance can cause coils to overwork, leading to premature failure. Review:

• Operator habits

• Water quality (use of a softener if required)

• Maintenance history

• Inconsistent practices can contribute to recurring heating issues.

  
  

Inspect Pressure or Flow Switches

Some dishwashers inhibit coil operation unless proper water flow or pressure is detected. If these sensors are faulty or clogged:

• The unit may not initiate heating.

• Cleaning or replacement may resolve the issue.

Examine Drain Valve Function

If the unit is draining prematurely or failing to retain water during the heating phase, the coil may not be submerged properly, resulting in dry firing and eventual burnout.

Use an Insulation Resistance Tester (Megger)

To thoroughly test the dishwasher heating coil insulation (especially in high-power systems), use a megohmmeter:

• Test from each terminal to ground at 500 V or 1000 V.

• A reading below 1 MΩ indicates insulation breakdown.

  
  

Faulty Contactors or Power Relays

In many commercial dishwashers, power to the heating coil is controlled through high-amperage contactors or relays. If these components are worn out, pitted, or stuck in the open position, the coil won’t receive the necessary voltage—even if everything else is functioning properly.

• You hear no clicking sound when heating should start.

• The coil tests fine, but there's no voltage reaching it.

• Use a multimeter to test relay output while the coil is supposed to be energized.

• Inspect contacts for carbon buildup or arcing damage.

  
  

Common Steps to Replacing Faulty Heating Coils 

Once you’ve confirmed the coil is faulty, replacing it is a relatively straightforward process, provided safety procedures are followed. Here’s how to do it:

Order the Correct Replacement Part

Obtain a coil that matches the original in voltage, wattage, and size. Check the model number of the dishwasher heating coil and consult with the manufacturer or authorized parts dealer. Using an incorrect coil may damage the unit or cause safety hazards.

Disconnect Power and Water

Again, ensure all power sources (both main and local disconnects) are off. Shut off the water supply to the unit to prevent accidental leakage.

Access the Heating Coil

Remove any panels or covers blocking access to the coil. This may require:

• Removing the lower kickplate

• Lifting out trays or racks

• Unscrewing protective covers

  
  

Remove the Faulty Coil

• Detach all wiring connectors from the coil terminals.

• Unscrew or unbolt the coil from its mounting bracket or flange.

• Gently remove the coil; avoid bending or forcing it out.

  
  

Install the New Coil

• Insert the new coil carefully into place.

• Apply a small amount of anti-seize compound on the bolts (if applicable).

• Tighten all fasteners securely, but avoid overtightening.

• Reconnect all electrical connectors firmly and double-check your work.

  
  

Restore Power and Test

• Reconnect the power supply and water lines.

• Run a test cycle and monitor the coil operation.

• Use a thermometer to verify correct water temperature.

  
  

Monitor Post-Installation

• Confirm temperature consistency.

• Listen for abnormal sounds.

• Watch for circuit breakers tripping (a sign of a wiring fault).

  
  

Inspect for Corrosion or Secondary Damage

Before installing the new coil, inspect the surrounding area for signs of corrosion, water damage, or burnt wiring. Replace or repair any damaged components to prevent future failures.

Clean the Coil Area

Use a soft brush or vacuum to remove dust, debris, or mineral deposits from the coil chamber and nearby parts. A clean installation site helps improve efficiency and prevents buildup that can damage the new coil.

Check Electrical Resistance

Use a multimeter to measure the resistance of the new coil before installation. This ensures the part is functional and matches the manufacturer’s specifications. An incorrect resistance could indicate a defective or mismatched part.

Secure Wiring with Clips or Ties

After reconnecting wires, use insulated clips or cable ties to secure them away from moving parts or areas exposed to high heat. This minimizes wear and risk of shorts.

Document the Repair

Make a note of the installation date, part number, and any other repairs done. This record helps with future troubleshooting and warranty claims.

Maintaining a fully functional dishwasher heating coil system in your commercial dishwasher is essential for sanitation and performance. Through careful troubleshooting and correct coil replacement, you can avoid service disruptions and costly technician visits. Always prioritize safety and follow manufacturer guidelines during repairs. Whether you’re dealing with inconsistent temperatures or complete heating failure, these steps will help you identify the problem and implement a lasting solution. Proper maintenance after installation will further ensure your dishwasher continues to operate efficiently and reliably.

Written by Allen Rode for PartsFeCa, your trusted source for a variety of high-quality commercial restaurant equipment, including commercial ice maker parts and dishwasher heating coil.