E15
Ruud
Thermostat / Call for Heat Input Fault
Boiler shows E15 and will not fire; may occur after thermostat wiring changes
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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
Shorted thermostat wires, incorrect 24V wiring, incompatible thermostat, failed low‑voltage fuse on control board
How to Fix / Troubleshooting
Safety first: Turn off power before working on thermostat or low‑voltage wiring.
- Inspect thermostat cable: Check for bare wires touching each other or metal surfaces. Repair or replace damaged cable.
- Verify connections: Ensure the thermostat is wired to the correct R and W (or T/T) terminals per the Ruud wiring diagram. Remove any unnecessary jumpers.
- Check control fuse: Many Ruud boards have a low‑voltage fuse. Inspect and replace with the exact same rating if blown. Investigate and correct the cause of the short before replacing.
- Test with a jumper: With power off, remove thermostat wires and temporarily jumper the call‑for‑heat terminals. Restore power. If the boiler operates without E15, the thermostat or its wiring is suspect.
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Repair Difficulty
Medium
3/5
Required Part
Low‑Voltage Fuse / Thermostat Circuit on Control Board
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