Lochinvar 502 - 2072, 402 - 2072 service manual Sequence of operation, OUT 123.8F129

Copper-fin II/IIE Boiler, Water Heater and Pool Service Manual

1 Service (continued)

Sequence of operation

Table 1A_Sequence of Operation - Space Heating and DHW

OPERATION	DISPLAY
1. The manual reset high limit (optional) must be closed before	HTR: Standby
any action will take place.	OUT: 123.8F(129)

2.Upon a call for heat the control turns on the appropriate HTR: Standby

pumps (system and boiler pumps for space heating; DHW OUT: 123.8F(129) pump for DHW call). The flow switch and low water cutoff

(if equipped) must close.

3.• The gas pressure switch(es) (if equipped) must close.

• The louver proving input must close.	HTR: Standby
• If the air pressure switch is open, the prepurge cycle then
begins by starting the combustion blower. Once started,	OUT: 123.8F(129)
the air pressure switch must close.

4. After the 15 second prepurge, the blower slows down and		HTR: PREPURGE
	the hot surface igniter (HSI) is energized. The HSI is heated
	for at least 20 seconds.	OUT: 123.9F(129)
5.	Once the HSI is hot, the trial for ignition begins with the	HTR: IGNITION
	opening of the gas valve.	OUT: 123.9F(129)
6. If the SMART SYSTEM control does not sense flame, then		HTR: POSTPURGE, PREPURGE
	it will lock out.	OUT: 123.9F(129)
7.	If the SMART SYSTEM control senses flame,
	it will fire the burner to maintain the set point. The	HTR: RUN STG: 1
	stages will fire as required to hold the actual temperature at
	the set point. If the boiler lights due to a space heating call for	OUT: 124.8F(129)
	heat, and the ramp delay function is active (default is
	disabled), the stages will be held to a series of increasing
	limits after the burner has lit.

8.If the space heating call for heat is active, and the DHW thermostat closes, the control will turn on the DHW pump,

wait 2 seconds, and then turn off the boiler pump. This will HTR: DHW STG 123

divert the hot water away from the heating zone(s) and send OUT: 177.8(180) it to the DHW tank instead. The control will then fire the

stages to maintain the outlet temperature to the DHW boiler set point.

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