E20
NTI
Safety Circuit Open (Limit / Cutoff Chain)
Boiler shows E20; may be labeled as 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 manual reset high limit, Tripped flue temperature limit, Faulty low‑water cutoff, Broken wiring in safety loop
How to Fix / Troubleshooting
Safety: Do not bypass safety devices. Determine and correct the cause of any trip before resetting.
- Identify safeties: Trace the safety loop on your NTI wiring diagram (high limit, flue limit, low‑water cutoff, etc.).
- Check each device: With power off, test continuity across each safety. Reset any manual reset devices after the boiler has cooled.
- Inspect wiring: Look for loose spade connectors, broken wires, or corrosion in the safety chain.
- Investigate root cause: If a limit has tripped, determine why (overheat, blocked flue, low water) and correct the underlying issue before restarting.
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Repair Difficulty
Hard
4/5
Required Part
High Limit Safety Thermostat
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