HELIX VX-399 Installation, Operation & Maintanance Manual page 68

1.4 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:
Lockout A01
after allowed
ignition trials
are exceeded
30 second
post purge
Yes
Setting
User Interface Display
68
Explanation
If flame 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 flame undetected after 3 seconds
boiler will de-energize Gas Valve and
enter post purge mode for 30 seconds.
Boiler will run provided all operational
and safety devices are within limits
Refer to for more information.
Control module adjusts firing 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.
P/N 240010943, Rev. C [09/07/2016]