Safety Shutdown

Figure 11: Wiring Diagram, 24 Volt Standing Pilot and Intermittent Circulation

Sequence of Operation

Normal Operation

1.When the thermostat call for heat, the vent damper will open (see paragraphs 17A through 17D). The circulator is started through a relay and at the same time the gas valve is energized allowing main gas flow and ignition of main burners.

2.Where condensation of flue gas is encountered in boiler flues a reverse acting circulator control should be installed to stop the circulator before the boiler water temperature drops to that which flue gas condensation may occur.

3.After the thermostat is satisfied the main valve will close and main burner flames will be extinguished.

The vent damper will close (see paragraph 17E).

1.High Limit Switch

In the event excessive boiler water temperature is developed the high limit switch will open interrupting power to the gas valve. The main burners will be extinguished immediately, and the vent damper will close at the same time, but the circulator will continue to operated. Normal operation will be resumed when the boiler water temperature drops to a point where the high limit switch closes.

2. Blocked Vent Switch

In the event excessive blockage in the vent system is developed the blocked vent switch will open interrupting power to the gas valve. The main burners will be extinguished immediately, the circulator will continue to operate, and the vent damper will remain open until the thermostat is turned off. The source of blockage must be corrected by trained and skilled personnel from a qualified service agency before resetting switch.

3. Flame Rollout Switch

In the event excessive blockage in the boiler section flue passageways is developed the flame rollout switch will open interrupting power to the gas valve. The main burners will be extinguished immediately, the circulator will continue to operate and the vent damper will remain open until the thermostat is turned off. If the flame rollout switch is activated do not attempt to place the boiler in operation. The source of blockage must be corrected and the flame rollout switch replaced by trained and skilled personnel from a qualified service agency.

4. Pilot

The thermocouple proves pilot flame and in the absence of such within 45-90 seconds causes the combination gas valve, which is equipped with a 100% shut-off provision, to be de-energized, thus, preventing main gas or pilot gas flow.