Heater starts then shuts off after a few minutes without any error code

Safety first: Turn off power before inspecting internal components.

• Check pump operation: Ensure the circulation pump runs continuously while the heater is on and is not controlled by a separate timer that shuts off early.
• Monitor filter pressure: A rapidly rising filter pressure can reduce flow and cause shutdown. Clean or backwash the filter.
• Verify sensor placement: Ensure water temperature sensors are properly installed and not located in a dead zone or near a hot return that could cause rapid temperature spikes.
• Observe behavior: Note whether the heater restarts automatically or remains off. This information helps a technician diagnose control issues.

If short cycling continues after stabilizing flow and verifying sensors, a technician should evaluate the control board and system sizing.