54
RT-SVX075C-EN
a. < 1.5 Vdc (0% ModBus Firing Rate)]: OFF
b. 1.5 – 2.0 Vdc (0.5% ModBus Firing Rate): Minimum
fire (Manifold pressure .20 to.30 in. w.c.)
c. 2.1 – 6.0 Vdc (1 - 56% ModBus Firing Rate):
Modulation linearized to firing rate (Modulating
Section Manifold pressure .25 to 3.50 in. w.c.)
9. If heating demand continues to increase and the analog
input signal exceeds 6.0 Vdc (56% ModBus firing rate),
and provided the air pressure switch is closed, the
VB1285 initiates a trial for ignition of the 2
nd
stage.
10. Burners ignite and cross light. Flame is sensed and
control continues the heating cycle.
11. Once the 2
nd
stage operation is verified, the 1
st
stage
modulation is reset to its minimum input rate.
12. The modulating gas valve is set as commanded by the
analog FIRING RATE input signal and will modulate
between 6.1 and 10.0 Vdc analog input (57 - 100%
ModBus firing rate), while maintaining operation of the
2
nd
stage at 3.50–inches w.c. manifold pressure.
13. The control remains in the high fire mode as long as the
firing rate signal is above 5.0 Vdc (46% ModBus firing
rate).
14. If the firing rate signal drops below 5.0 Vdc (46%
ModBus firing rate), the 2
nd
stage section will shut-off
and the 1
st
stage will continue to operate and modulate
in response to changes in analog signal voltage.
15. System will continue in the run state until the heat
enable contacts open or the analog input signal drops
below 1.5 Vdc (0.5% ModBus firing rate) signal.
16. When call for heat is removed, 1
st
stage gas valve
closes and modulating actuator is moved to Park
position, and the inducer is operated for a post purge
period of 60 seconds [PPuurr].
17. Control returns to the standby mode [OOffff].
Ignition and Operational Failures During
a Call for Heat
1. If flame is not detected on the original ignition trial
[AA0011], the controller enters an inter-purge period of 30
seconds [rrEEtt] and then will initiate another ignition trial.
The control will repeat this sequence for up to 4 ignition
trials.
2. If four consecutive failed ignition trials occur, control will
go into lockout [EE0011].
3. If flame is lost during an operating cycle [AA0022], the
controller will operate same as in Step 1.
4. Limited low fire [AA0044] will happen if flame loss at low fire
results in an auto-adjustment that limits the burner turn
down during the rest of the current call for heat.
5. Lockout will also occur for the following:
a. Open Limit or Rollout Switch [EE0022].
b. Low air pressure sensor reading is air pressure
does not correspond to gas pressure [EE0044].
c. No R-W Enable [EE0099].
6. If the combustion air pressure switch opens (blocked
vent or other airflow restriction) during heater operation
with a continued call for heat, the control will lockout for
one hour and then initiate a trial for ignition sequence.
7. Lockout will occur for any lockout error on either control
and terminate heater operation for the duration of the
lockout timing.
8. If no call for heat is present, controller is in the Off
mode [OOFFFF].
Recovery from Lockout (E Code)
1. If the call for heat (thermostat or heat enable closed) is
still present one hour after a lockout occurs, the control
will automatically reset and initiate a call for heat
sequence.
2. Control may also be reset manually by removing power
to the controller for 10 seconds and restoring power to
controller.
Display Code Code Type Description Additional Comments and Notes
888888 10s L/O Board Failure (Up to 10 seconds at power up) Verify 24 Vac signal input at connector J6.
OOFFFF Status UP Mode: Burner state = Off
PPuurr Status UP Mode: Burner state = Purge
II66nn Status UP Mode: Burner state = Ignition
HHEEAA Status UP Mode: Burner state = Warm up
rruunn Status UP Mode: Burner state = Run
rrEEtt Status UP Mode: Burner state = Retry (with AA0011 or AA0022) Retry delay following either a failed ignition or a flame
loss.
AA0011 Alert Failed ignition attempt
AA0022 Alert Lost Flame Ignition was successful but then flame disappeared.
Unit Start-Up
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