Patterson-Kelley MOD-04 - Manual (Page 32)

Modu-Fire
®
Gas-Fired Boiler Maintenance
29
minal 9 of the Combustion Control is energized.
This opens the main gas valve and energizes the
air gas ratio control. The 15 second "Main
Flame Establishing” period begins. If pilot
flame has not been established, the unit will
lock out on pilot flame failure.
13. After the 15 second “Main Flame Establishing
Period” if flame has been established, Terminal
8 of the combustion control is de-energized,
closing the pilot valve. Terminal 15 is ener-
gized, providing power to the modulating con-
trol of the boiler. If main flame has not been es-
tablished, the unit will lock out on main flame
failure.
14. The unit modulates between the low fire setting
and the high fire setting to maintain the desired
outlet water temp set point.
15. When the load is below the low fire rating of the
boiler the boiler will continue firing and the out-
let water temperature will rise until it reaches
operating limit setpoint value. At this point the
operating control switch opens and the combus-
tion control is de-energized at Terminal 6 and
the indicator for HEAT is turned off. This ac-
tion also de-energizes Terminal 9 thus closing
the main gas valve and the air gas ratio control
valve. Terminal 14 is energized which applies
power to the close terminal of the air damper
motor. The air damper closes.
16. When the water temperature is reduced by the
load on the system, the operating control switch
will close again. The operating sequence will
recycle to step 5, provided the limits on water
flow, gas pressure and high temperature are all
met.
5.6 T ROUBLESHOOTING
Loss of Power
In the event of loss of power, the entire boiler sys-
tem is de-energized, closing all automatic valves
and halting all boiler operations. When power is
restored the sequence of operation will resume at
Step 5, provided that all the limits are satisfied.
Loss of Water Flow
When the "Water Flow" indicator is illuminated,
there is insufficient water flow to close the switch,
and burner operation is interrupted. When water
flow is re-established, the sequence returns to Step
2, provided that the other limits are satisfied.
Gas Pressure
When the "Gas Press" indicator is illuminated, there
has been either insufficient gas pressure or the gas
pressure to the manifold is too high for safe and
proper operation of the boiler. The power to the
programmer will be interrupted.
If a gas-supply shut-off valve is closed for any rea-
son, a low gas condition will result.
When gas pressure is restored, the "Gas Press" indi-
cator will remain on and the boiler will remain
locked out until the gas pressure switch is manually
reset.
In the event of a high gas manifold pressure condi-
tion, the “Gas Press” indicator will illuminate indi-
cating a potential air gas ratio control failure. This
must be corrected by factory-trained personnel be-
fore restarting the boiler.
Once the switch is reset, the sequence returns to
Step 3, provided that the other limits are satisfied.
High Water Temperature
When the boiler water has exceeded both the operat-
ing and high-limit temperature, power to the pro-
grammer is interrupted. When the water tempera-
ture falls below the high-limit temperature, the
boiler will remain locked out until the switch is
manually reset. Once the switch is reset, the se-
quence returns to Step 4 to await heat demand pro-
vided that the other limits are satisfied.
Low Air
If the "Low Air" indicator remains on for longer
than 20 seconds, there is insufficient airflow through
the burner. An extended low air indication does not
mean that the low air switch is defective.