Fireye NX6100 F41 subset 4: boiler pressure limit exceeded, what to check?

Question

Our Fireye NX6100 controller tripped F41, subset 4, on the boiler. The pressure trend was rising before the trip. What should I check first to troubleshoot this?

Top answer · Written by InduQT from the fault guide and manufacturer manuals cited below · Oct 28, 2026

The Fireye NX6100 F41 fault indicates either a boiler pressure/temperature sensor issue or that the boiler's measured value exceeded a safety limit. Subset 4 specifically points to a real over-pressure or over-temperature event. This often occurs when steam demand drops suddenly or the burner remains at high fire, causing the pressure to rise to the limit.

Likely causes and checks

1Real over-pressure or over-temperature

Points to it: The boiler's measured pressure or temperature went above the controller's safety limit. This is a process event, not an instrument fault, and should be treated as a real over-pressure until proven otherwise.
Check: Review the steam pressure or water temperature trend and the firing rate immediately before the trip. Verify the modulation setpoint and PID control parameters against the safety limit.

2Sensor or wiring fault

Points to it: The pressure/temperature sensor may not be responding correctly, or there's an issue with its wiring. This would typically manifest as the pressure reading jumping, reading full scale, or zero.
Check: Inspect the sensor wiring and its power supply. Ensure that no analog input to the controller exceeds 5 V.

3CANbus fault

Points to it: A communication fault on the CANbus could prevent the controller from receiving correct sensor data. Other CAN devices might also show errors if this is the case.
Check: Examine the CANbus wiring and termination to the sensor for any issues.

Next check: Since the fault is F41 subset 4 and the pressure trend was rising, prioritize checking for a real over-pressure condition by reviewing the boiler's operational data and control settings.

Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.