NTI Low Load / Minimum Firing Rate Mismatch

Boiler cycles on and off when only a small zone or single radiator is calling for heat

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.

Possible Causes

Boiler minimum output higher than zone load, No bypass or buffer tank, Aggressive control settings, Oversized circulator

Safety: This is primarily an efficiency and wear issue, not an immediate hazard.

Adjust controls: Increase differential and adjust outdoor reset to lengthen run times.
Hydraulic balancing: Throttle flow to small zones or add a bypass to maintain minimum flow through the boiler.
Add buffer: For very small loads, consider adding a buffer tank sized per NTI recommendations.

Medium 3/5