Heater shows E15 and will not start; often associated with internal safety chain issues.

Safety first: Disconnect power and allow the heater to cool. Do not bypass safety devices for normal operation.

Step-by-step checks:

• Locate safety chain: Using the Pahlen wiring diagram, identify all safety devices wired in series (high limit, flue limit, pressure switch, etc.).
• Check continuity: With power off, test continuity across each safety device individually. A device that remains open at normal temperature/pressure is likely faulty.
• Inspect wiring: Look for loose spade connectors, broken wires, or corroded terminals in the safety loop. Repair as needed.
• Reset manual limits: Some limits have manual reset buttons. Once the heater is cool and the cause of the trip is addressed, press to reset.

When to stop: If you cannot identify which safety is open or if multiple devices are tripping, have a technician evaluate the heater for underlying overheating or pressure problems.