PB Heat Gas Boiler manual Electrical, 3 Boiler Control Board Wiring Schematic

ELECTRICAL

e)The main gas valve is then energized to allow gas to mix with the combustion air.

f)If the main flame is not detected in 5 seconds, the gas valve closes and the combustion fan goes into post-purge. Otherwise, the combustion fan stays at the ignition speed for the length of the flame stabilization period. (10 to 25 seconds).

g)After the flame stabilization period is complete, the combustion air fan ramps down to its low fire setting. Then the boiler will begin to modulate depending on the supply temperature to maintain the set point temperature.

h)As the supply temperature approaches the set point, the combustion control will reduce the input rate. The supply temperature will continue to climb to about 7°F above the boiler set point before it cycles off.

i)The differential is applied from this point. For example if the boiler set point is at 180°F with a 10°F differential, the supply temperature will reach 187°F before shutting down. It will not re-start until the supply temperature drops below 177°F.

Figure 6.3: Boiler Control Board Wiring Schematic

27