A20
IVT
Safety interlock circuit open
Furnace indicates safety chain open; unit will not start
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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 high limit switch, Tripped manual reset safety, Loose wiring in safety loop, Faulty door interlock switch (if equipped)
How to Fix / Troubleshooting
Safety: Turn off power. Do not bypass safety devices.
- Identify safety devices: Using the IVT wiring diagram, locate all devices in the safety chain (high limit, flue limit, door switch, etc.).
- Check manual reset limits: Some IVT models have manual reset buttons on high limit or flue limit switches. After cooling, press the reset button until it clicks.
- Inspect wiring: Follow the safety loop wiring, checking for loose spade connectors, broken wires, or corrosion.
- Test continuity: With power off, use a multimeter to check continuity through each safety device. Replace any that remain open at normal temperature.
If a safety device trips repeatedly, find and correct the underlying cause (overheating, blocked flue) rather than just resetting it.
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Repair Difficulty
Medium
3/5
Required Part
IVT high limit safety switch
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