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Raypak Low Ambient Temperature Lockout

Raypak heat pump or pump/heat combo displays LO or LOW TEMP and will not heat; unit may run fan only.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Outdoor temperature below Raypak operating range, Faulty ambient temperature sensor, Sensor wiring damage, Control board misreading sensor

How to Fix / Troubleshooting

Safety first: Turn off power before accessing the control compartment or sensors.

  • Verify outdoor temperature: Compare the actual outdoor temperature with the Raypak display. If it is genuinely too cold, the unit is protecting itself; wait for warmer weather.
  • Check sensor placement: Locate the ambient temperature sensor (usually clipped near the air intake). Ensure it is not touching hot surfaces or exposed to direct sunlight, which can skew readings.
  • Inspect wiring: Follow the sensor wires back to the control board. Look for rodent damage, cuts, or loose connectors. Reseat the plug on the control board.
  • Test/replace sensor: Using the service manual, compare the sensor resistance to the temperature chart. If readings are out of range, replace the ambient temperature sensor with a Raypak‑approved part.
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Repair Difficulty

Medium 3/5

Required Part

Ambient Temperature Sensor
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