Heater will not start; display shows E01 shortly after a heat demand is issued.

Safety first: Turn off electrical power to the Pahlen pool heater at the breaker and close the gas shutoff valve before working on the unit. Allow the heater to cool completely. If you ever smell gas, evacuate the area and contact your gas supplier or a licensed technician immediately.

Step-by-step checks:

• Verify gas supply: Ensure the external gas shutoff valve to the Pahlen heater is fully open. Check that other gas appliances on the same line work normally. If not, there may be a supply or regulator issue.
• Inspect burner compartment: Remove the front service panel of the Pahlen heater. Look for debris, rust flakes, or insect nests around the burner tray and combustion chamber. Clean gently with a soft brush and vacuum.
• Check ignition electrode: Locate the ignition electrode on the burner assembly. Inspect the ceramic insulator for cracks and the tip for heavy carbon buildup. Clean the tip with fine emery cloth. Ensure the electrode gap and position relative to the burner follow the Pahlen service manual.
• Check flame sensor (if separate from igniter): Remove the flame sensor rod and clean it with fine steel wool or emery cloth to remove oxidation. Reinstall firmly and ensure the wiring connector is tight.
• Verify wiring: Inspect the harness from the control board to the gas valve, ignition electrode, and flame sensor for loose connectors, corrosion, or damaged insulation. Reseat any loose plugs.
• Restore power and test: Open the gas valve, restore power, and call for heat from the pool controller or thermostat. Observe through the sight glass: you should see sparking and then a stable blue flame. If E01 returns and there is no ignition, the gas valve or control board may be faulty and should be tested by a qualified technician.

When to stop: If you are not comfortable working around gas components or if the heater repeatedly fails to ignite after cleaning and basic checks, contact a licensed pool heater technician familiar with Pahlen units.