The air pressure switch confirms that the fan is providing sufficient combustion air before gas supply is allowed. If the correct contact does not change state, the BMS stops the sequence.
The fan does not start
Check the electrical power supply to the motor, the contactor, the overload relay, the inverter where applicable, and the command from the BMS.
The fan is running but the pressostat does not activate
Possible causes include a clogged pressure tube, incorrect connection to the ports, low actual air pressure, or an incorrect setpoint.
Damper or mechanical issue
If the damper does not reach the correct position, the pressure or air flow may be insufficient. Check the position of the servomotor and the mechanical linkage.
Intermittent fault
Loose contacts, vibrations, or contamination in the pressure switch can cause a momentary loss of signal.
Important detail
Do not arbitrarily increase the setpoint or bypass the pressostat. It is a critical component of the burner's safety chain.