Display shows 'LO' and heater will not fire or shuts down; may be intermittent.

Safety first: This involves line voltage (120/240V). Turn off power at the breaker before opening the electrical compartment. Only qualified persons should measure live voltage.

Steps to address LO error:

• Confirm supply voltage: Verify that the heater is wired for the correct voltage (120V or 240V) per the rating plate. Mismatched wiring can cause LO errors.
• Inspect wiring connections: With power OFF, remove the electrical access cover and check all lugs and wire nuts at the terminal block and transformer primary. Tighten any loose connections.
• Check wire size and run length: Long runs with undersized wire can cause voltage drop under load. Compare installed wire gauge to Raypak installation requirements.
• Measure voltage: With power ON (if qualified), measure line voltage at the heater terminals and compare to nameplate. Also measure secondary (24 VAC) output from the transformer. Low readings indicate supply or transformer issues.
• Replace faulty components: If the transformer output is low with correct input, replace the transformer. If voltages are correct but LO persists, the control board may be misreading voltage and require replacement.

Warning: Do not operate the heater with known low voltage; it can damage motors and controls.