Troubleshooting Guide
CLCH-SVX014B-EN 29
VB1285 Sequence of Operations
1. A call for heat is initiated by the rooftop unit control
through a digital Modbus signal or the analog
thermostat.
2. The VB1285 control will then go through a system
check to ensure that the high temperature limit and
rollout switches are closed, the air pressure switch is
open, and the modulating valve is positioned correctly.
3. The control will then enter the pre-purge cycle, where
the inducer will run at the programmed purge
pressure. During this cycle, the control will look for the
air pressure switch to close and open at the correct
settings.
4. Once the system check and pre-purge cycles are
complete, the control will enter the ignition cycle.
a. The modulating valve and inducer will go to their
“light off” settings.
b. The DSI ignition module will be energized and the
spark ignitor will activate.
c. The redundant safety valve will open, allowing gas
flow.
d. The burners will ignite and the control will receive
a signal from the flame sensor.
e. The spark ignitor will remain active for the duration
of the ignition cycle, regardless of flame status.
5. If flame is not established during the ignition cycle, the
control will repeat the pre-purge and ignitions cycles
Table 6. Troubleshooting guide for VB1285 modulating control
Failure Code Description of Symptom Actions
E08 3 or 4 Flame is detected without call for heat
1. Ensure there is no voltage to gas valve—repair/replace wiring if
voltage is present.
2. If voltage is not present, check for gas flow. If gas is flowing, verify
line and manifold pressures before replacing valve.
E04 28
Air pressure sensor reading low and/or
pressure switch failed to open
1. Failed combustion blower.
2. Check pressure hoses for leaks or blockage.
3. Check for blockage in the inducer barb fitting.
4. Check for condensate accumulation in the pressure switch and
hose.
5. Check the pressure switch wiring.
6. Replace the pressure switch.
E05 29
Air pressure sensor reading high and/or
pressure switch failed to close
1. Check wiring to the pressure switch and draft inducer.
2. Replace the pressure switch.
E01 11 Failed ignition, retries have been exhausted
1. Verify gas supply available and manifold pressure is correct.
2. Verify the gas valve is in the ON position.
3. Verify that a spark in present; if not check igniter for debris
between the electrodes, for cracked ceramic and check ignition
wire for cracks.
4. Check to see if the sensor ceramic is cracked or if the electrode
wire is coated with dirt or oils.
5. Check to see if the flame sensor wire is connected properly and not
grounded due to wire abrasions.
6. Check for air leaks.
7. Check for re-circulation of flue product.
E02 7 Primary limit or limit switch failure
1. Determine which switches are open using an OHM meter.
2. If limit switch is open, check temperature rise and airflow over the
heat exchanger.
3. If high limit does not reset with proper airflow, change limit.
4. If rollout switch is open check for flue vent blockage or air leaks
in the cabinet.
5. Reset the rollout switch and observe the flame for signs of rolling
out.
E18 Unexpected flame (split manifold burners)
1. Unplug flame sensor, replace sensor if error corrects.
2. Is there voltage to the gas valve with no call for heat? Remove
voltage source, rewire.
3. Check for excessive gas line pressure. Install regulator if high gas
pressure.
4. Replace gas valve.
5. If rollout switch is open, check for flue vent blockage or air leaks
in the cabinet.
6. Reset the rollout switch and observe the flame for signs of rolling
out.
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