Hobart E-05 Ignition Failure. Gas Burner Won't Light Fix

Error Code: Hobart E-05

What it means: The control board opened the gas valve but did not receive a flame-prove signal within the ignition safety period. The board sees 24VAC sent to the gas valve, the valve clicks open, gas flows into the burner chamber, but the flame sensor or thermocouple reports no heat. After three to five failed ignition attempts (depending on the model), the board locks out and displays E-05.

This error applies to gas-heated Hobart dishwashers. It occurs in two distinct contexts. On conveyor dishwashers (CL, CX, FT series), the booster heater fails to ignite. On door-type machines (AM-14, AM-15, CLe), the wash tank or rinse burner fails to fire. The diagnostic approach is the same, but the component locations differ.

Hobart uses spa-type spark igniters rather than hot-surface igniters. A spark jumps from the electrode to the burner ground. If the gas is flowing and the spark is present, the gas ignites. The flame sensor then detects the flame and tells the board to keep the gas valve open. If any link in this chain breaks, you get E-05.

The board does not know why the flame failed. It only knows the valve opened and no flame was detected. You need to determine whether the problem is no gas, no spark, or a bad sensor.

Common Causes

• Gas supply off or restricted. The most common cause. Someone closed the gas shutoff valve during maintenance, or the supply pressure dropped below the minimum required by the burner. Natural gas systems need 5 to 7 inches water column at the burner inlet. Propane (LP) systems need 10 to 12 inches water column. Low pressure can cause the gas valve to open but deliver too little gas to light.
• Gas type mismatch. The machine is configured for natural gas but connected to a propane supply (or the reverse). The orifice sizes and gas valve springs differ between fuel types. Using the wrong setup produces either too much or too little gas, and the burner will not light properly.
• Fouled or misaligned spark electrode. The spark electrode sits in the burner path. Grease, carbon, and food soil build up on the electrode tip over time. The gap between the electrode tip and the ground strap should be 1/8 inch. A wider gap produces weak sparks. A narrower gap causes the spark to short directly to ground instead of jumping across the burner.
• Cracked or shorted spark cable. The high-voltage cable from the ignition module to the electrode breaks down over time. Oil and heat damage the insulation. The spark then jumps through the cable jacket to ground before reaching the electrode. This produces no visible spark at the burner.
• Failed ignition module. The ignition module generates the high-voltage spark pulses and monitors the flame signal. If the module receives no flame signal within the trial period, it stops sparking and locks out. A dead module produces no spark at all.
• Dirty or failed flame sensor or thermocouple. Hobart uses either a flame rod (flame rectification) or a thermocouple (millivolt) to detect flame. Flame rods collect carbon deposits that insulate the rod from the flame signal. Thermocouples develop internal resistance or fail open. The board reads zero flame signal and locks out.
• Gas valve problems. The gas valve coil can fail open or short. The valve may click but not fully open, or it may open but the internal diaphragm may stick shut. Coil resistance should measure between 20 and 60 ohms for most Hobart gas valves. An open reading (OL) means the coil is burned out.
• Hi-limit thermostat tripped. The hi-limit thermostat sits near the burner. If the burner chamber overheated in a prior cycle, the limit may have tripped open. A tripped limit cuts power to the gas valve circuit, so the valve never fires. Test for continuity across the limit terminals. If no continuity, the thermostat needs to be reset or replaced.
• Door interlock micro-switches. The control board will not fire the burner if any door or safety interlock is open. Conveyor machines have multiple interlocks along the hood. A misaligned or failed micro-switch prevents the ignition sequence from starting.

Step-by-Step Fix

1. Confirm the gas supply is on and at the correct pressure. Locate the gas shutoff valve for the dishwasher. Verify it is fully open. Not partially open. Fully open. Connect a manometer to the burner inlet test port. For natural gas, you need at least 5 inches water column with the machine calling for heat. For LP, you need 10 to 12 inches. Low pressure at the machine usually means the main supply is undersized, the regulator at the building inlet is faulty, or there is a partial blockage in the gas line.

2. Check the machine gas type label. Look for a tag near the gas valve or data plate. It will say Natural Gas or LP/Propane. Compare it to the gas supply. If they don’t match, you need an LP conversion kit from Hobart. Do not attempt to operate the machine on the wrong gas type.

3. Inspect the spark electrode. Disconnect power to the machine. Remove the burner access panel. Locate the spark electrode. Look for visible cracks in the ceramic insulator. Check the electrode gap. The gap should be 1/8 inch between the electrode tip and the ground strap. Adjust by bending the ground strap. Clean the electrode tip with fine emery cloth to remove carbon and grease.

4. Test the spark cable and ignition module. Reconnect power and start a cycle that calls for heat. Watch the spark electrode through the sight glass or access port. You should see a steady snap of blue-white sparks at the electrode tip. No spark means the cable, module, or wiring is bad. Replace the spark cable first (it is the cheaper and more common failure). If a new cable does not fix the no-spark condition, replace the ignition module.

5. Check the flame sensor. Locate the flame sensor. On AM-14 and AM-15 machines, it is a metal rod positioned in the burner flame path. Remove it and clean the rod with emery cloth or steel wool. Reinstall and retest. If the machine has a thermocouple instead of a flame rod, test the thermocouple output with a millivolt meter. A good thermocouple produces 25 to 35 millivolts when heated with a propane torch. Below 15 millivolts, replace the thermocouple.

6. Test the gas valve. With power on and the machine calling for heat, measure voltage at the gas valve coil terminals. You should read 24VAC. If no voltage, the issue is upstream (board, thermostat, or interlock). If 24VAC is present but the valve does not click, test coil resistance with an ohmmeter. Disconnect the coil wires first. Good coils read 20 to 60 ohms. Open or short coils need replacement.

7. Check the hi-limit thermostat. Locate the hi-limit thermostat on or near the burner. Disconnect power. Place a multimeter in continuity mode across the thermostat terminals. A closed thermostat shows zero ohms. An open thermostat shows OL (infinity). If open, check whether the thermostat has a manual reset button on top. Press it to reset. If it trips again immediately, the burner is overheating and you need to find out why. If the thermostat is non-resetable, replace it.

8. Test the door interlock switches. Start a cycle and check that the display shows a closed door or conveyor hood. Open the door and confirm the display changes. If the display does not change, the door switch is not closing. Adjust the switch actuator or replace the switch.

9. Reset the control board. After fixing the identified issue, turn off the main circuit breaker for the machine. Wait 60 seconds. Turn the breaker back on. This clears the E-05 lockout. Start a wash cycle and confirm the burner ignites and stays lit through the full cycle.

Hobart Error Code Reference Table

When to Call a Professional

Call a licensed commercial kitchen technician if you have checked all the above and the E-05 still returns. A few situations require a pro:

You find the gas pressure is below spec and the building regulator needs adjustment. Tampering with gas regulators is unsafe and often illegal without a license.

The spark electrode ceramic is cracked and embedded in the burner housing. Removing a broken electrode sometimes requires drilling out the old one without damaging the burner tube.

The control board needs replacement. Hobart boards require proper programming for specific machine configurations. A technician with a Hobart service kit can set the board parameters correctly.

You smell gas at any point during troubleshooting. Stop immediately, shut off the gas supply, open the kitchen windows, and call the gas utility or a qualified technician. Do not operate the machine until a professional clears the system.

Technician tip: When you call for service, tell the dispatcher “E-05 error on a Hobart [your model]. I have confirmed gas pressure is good and the spark electrode is clean.” This saves the tech time and saves you money on the service call.