4
Figure 11.4: Outdoor reset Curve
7)
The sequence of operation for a CHG series boiler on a call for heat from a thermostat is as described below:
a) When power is first turned on, 120V is provided to the MCBA, the combustion fan and the LWCO trans-
former. A separate 50VA transformer, connected directly to the MCBA, powers all other low voltage circuits.
b) For the first few seconds after power-up the control module goes through a self check.
c) When there is a call for heat, the control module checks to make sure the air pressure switch is open. If it is, the
combustion fan will be energized and will ramp up to ignition speed. When the air pressure switch closes, a 10
second prepurge is activated.
d) After the prepurge, the control module energizes the gas control valve and the spark for 4.5 seconds. If a
flame is established and proved, the control allows the flame to stabilize for 5 seconds at the combustion fan
ignition speed setting. If the flame fails to prove, the control module will attempt to light the burner 4 more
times. If a flame is still not established, the control will lockout.
e) Once the flame stabilization period has ended, the MCBA allows the burner to modulate. The actual firing rate
is dependent upon the measured current and recent differences between the set point temperature and the supply
temperature. If an outdoor sensor is connected to the control module and the boiler is responding to a call for
heat, the set point temperature will be determined by the outdoor reset curve shown in Figure 11.4.
f) Once the set point temperature is reached, the MCBA will turn the burner off and allow the combustion fan to
operate in postpurge for 35 seconds before it turns off.
g) The central heating pump will continue to operate until the room thermostat has been satisfied.
h) A demand for domestic hot water (DHW) is given priority on CHG series boilers. If a call for DHW is received
while the boiler is responding to a call for heat, the heating circulator is deenergized until the call for DHW is
satisfied.
Summary of Contents for CHG CHG150
Page 25: ...25 Figure 8 3 Piping Method 1 Heat Indirect Water Heater Figure 8 2 Piping Method 1 Heat Only ...
Page 29: ...29 Figure 8 8 Piping Method 2 Heat Only Figure 8 9 Piping Method 2 Heat Indirect Water Heater ...
Page 36: ...36 Figure 9 1 Wiring Connections Diagram ...
Page 37: ...37 Figure 9 2 Ladder Diagram ...
Page 38: ...38 Figure 9 3 Wiring of Isolation Relay for Control of Two Heating Circulators ...
Page 40: ...40 CHG Series Lighting and Operating Instructions ...
Page 46: ...46 Figure 11 2 Basic Menu Tree ...
Page 54: ...54 SERVICE RECORD DATE SERVICE PERFORMED ...
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Page 69: ...69 SERVICE RECORD DATE SERVICE PERFORMED ...
Page 70: ...70 SERVICE RECORD DATE SERVICE PERFORMED ...
Page 71: ...71 SERVICE RECORD DATE SERVICE PERFORMED ...
Page 72: ...9EARS IN 3ERVICE 3ERVICE HARGE AS OF 2ETAIL 0RICE O HARGE ...