E04
Raypak
High Limit / Temperature Sensor Error
Boiler shows E04; high limit or temperature sensor error on some Raypak models.
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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
Open or shorted high limit sensor, Loose sensor wiring, Overheating due to low flow, Control board input fault
How to Fix / Troubleshooting
Safety: Turn OFF power and allow the boiler to cool.
Steps:
- Check system water flow and circulator operation.
- Inspect the high limit sensor and wiring for secure connections.
- Reset any manual high limit if present.
If E04 recurs, have a technician test the sensor resistance and replace the sensor or control as needed.
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Repair Difficulty
Hard
4/5
Required Part
High Limit Sensor
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