UTICA BOILERS UBSSC-050 Installation, Operation & Maintanance Manual page 60

2.4 Sequence of Operation
Operational State
After 2 seconds
Flame
Yes
Detected?
No
Gas Valve
Energized
After 3 seconds
Flame
No
Detected?
Yes
Heat Demand
Met?
No
No
Simultaneous
DHW + CH
Demand?
See Max DHW
Priority Time
Yes
DHW
Priority
Mode
APPENDIX A - CONTROL MODULE
Lockout
Error A21
Note:
5 Ignition
trials,
then
Lockout A01
30 second
post purge
Yes
Setting
User Interface Display
60
Explanation
If fl ame detected before Gas Valve
opens during ignition boiler will
lockout.
Please refer to troubleshooting
guide.
Gas Valve energized to deliver air/
fuel to burner.
If fl ame undetected after 3 sec-
onds boiler will de-energize Gas
Valve and enter post purge mode
for 30 seconds.
Ignition attempted 5 times before
lockout.
Boiler will run provided all op-
erational and safety devices are
within limits
Refer to for more information.
Control module adjusts fi ring rate
according to heating demand.
When Boiler detects demand met,
will enter post purge mode then
standby mode.
If simultaneous demand for
Central Heat and DHW, boiler will
enter DHW Priority Mode.
Priority mode limits amount of
time boiler can run in DHW mode
to meet CH demand.
Max DHW Priority Time setting
determines maximum time
allowed for DHW heating mode.
Please refer to section Appendix A
section 1.5 for more information.