User Guide

Part number 550-100-193/0817
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CONDENSING GAS BOILER — 70/110/155 Advanced Manual
Figure 18 Control sequence of operation
Display
status
text
Control action
(also see Figure 19, page 42)
POWER
UP
s Check the boiler model listed on the power-up screen. If it is not correct, turn off the boiler. See page 43 for in-
structions to change setting.
s When power is turned on, the screen lists sensors that are detected. If any sensor is not listed, make sure it is con-
nected correctly. Turn off power and restart.
Standby
s Standby - no calls for heat.
s Toggles through no dots, 1 dot, 2 dots, then 3 dots while in standby (wrench symbol will show instead if mainte-
nance is needed).
Blower
ON
s Call for heat detected.
s Display on with BLUE light (space heating) or PURPLE light (DHW).
s Start min/max timers if more than one system is calling - highest priority starts first.
s Start circulators for this priority based upon settings.
s Calculate target temp — If sensor temp is below target temp, begin firing sequence.
s Blower to ignition speed for prepurge.
Ignition
s After prepurge times out, begin ignition cycle.
s Activate gas valve and ignition spark.
s Continue ignition spark for ignition period.
s Turn off spark and use electrode to check for flame signal.
Space
Heating
s Flame detected.
s Release boiler to modulation.
s NOTE: If flame is not detected, the gas valve is turned off, blower turns on (postpurge), and control starts cycle
again. After 5 failures, the control waits 60 minutes, then tries again.
s If priority timer times out, switch to next priority and start priority timer.
s If demand satisfied, go to postpurge.
DHW
Heating
s Flame detected.
s Release boiler to modulation.
s NOTE: If flame is not detected, the gas valve is turned off, blower turns on (postpurge), and control starts cycle
again. After 5 failures, the control waits 60 minutes, then tries again.
s If priority timer times out, switch to next priority and start priority timer.
s If demand satisfied, go to postpurge.
Blower
OFF
s Demand satisfied (temperature reaches target temperature or limit setting).
s Gas valve off.
s Blower to ignition speed for postpurge.
s Return to standby after purge.
Maintenance
s Display flashes BLUE, toggling between graphic screen and maintenance screen (occurs if maintenance schedule
timer times out).
s Will show during standby only.
s Boiler operates as normal.
Error/fault
s Display turns RED due to error or limit event.
s Flashing display means lockout condition.
WWSD
s Warm weather shutdown - the boiler will not be allowed to fire on space heating if the outside temperature is
greater than the WWSD setting.
s DHW operation is not affected by WWSD.
Control operation