A burner may ignite normally but remain at low fire or stop before reaching the required load.
Demand signal
Check if the PLC, BMS, or controller is actually sending a command for a higher load.
Servomotor and feedback
The actual air and gas position is compared against the command. If the actuator does not follow, modulation is restricted.
Load limits
Temperature, boiler pressure, draft, or another process limit may be restricting the load without an actual fault.
Gas pressure limitation
If the pressure drops as the load increases, the BMS may not allow further output increase.
Commissioning curve
After an actuator change or adjustment, it must be verified that the modulation curve is correctly parameterized.
