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HI-DELTA Model 902
The black (hot) wire leads you directly to the Main Power Switch. This switch is located at the bottom right-front corner
of the control compartment. When the main power switch is placed in the “ON” position, both the 120 v and 24 v terminal
blocks on the Main Circuit Board will be powered and the power light will turn on. When the Auto On- Off switch is
turned ON, the following 24 v safety components are immediately energized: Low Water Cut-off, Blocked Vent Switch,
Manual Reset Limit Control, Low Gas Pressure Switch (optional) and the High Gas Pressure Switch (optional). At this
point if all the preceding safety switches are closed, then Relay No. 1 (n.c.) will be energized and the safety light will turn
off. The boiler is now ready for a call for heat.
When STAGE 1 calls for heat, the CALL FOR HEAT LIGHT will turn on. The Economaster Board will be energized and the
pump will turn on. If the pump generates enough flow to activate the flow switch, the flow light will turn on, power will be
applied to the thermostat terminal of the Ignition Module and the Blower will activate. The Air Pressure Switch will close,
and the pressure switch terminal on the Ignition Module will be energized the blower light will turn on. The Unit will now
undergo a 15 second pre-purge. After the pre-purge cycle, Hot Surface Igniter will heat up. The heat-up period takes
about 30 seconds after which a trial for ignition is initiated. During the trial for ignition, which lasts for four seconds,
power is applied to Firing Valve No. 1. If within four seconds, the Remote Sensor establishes flame rectification, then
Firing Valve No. 1 stays open and the Stage 1 light will turn on. Power from the Valve terminal will power Relay K2 and K3.
Power will be applied to Time Delay Relay No. 1 and after ten seconds Firing Valve 1A will turn on.
When Stage 2 calls for heat, power will pass through Time Delay Relay No. 2, then after 10 seconds through Relay K4,
and then Firing Valve No. 2. The Stage 2 light will come on also, at this time.