MACH® Series
Gas-Fired Boiler
Maintenance
Page 31
5.3
A
FTER
A
LL
R
EPAIRS OR
M
AINTENANCE
1. Follow "Pre-Start Check List" (Section 3.10) and
all "Safety Checks" (Section 3.11).
2. Check gas pressure. (Section 3.12.2.)
3. Perform combustion check. Adjust gas flow if
necessary. (Section 3.12.4.).
5.4
S
EQUENCE OF
O
PERATION
1. In order for the boiler to start, the following limits
must be satisfied:
a)
Low water level control
b)
High & low gas pressure switches
c)
High temperature limit
2. When the On/Off (Main power) switch is turned
on, power is provided to the boiler control,
combustion blower and the gas valve relay board.
3. When the water temperature is below the control
setpoint, a heat request is generated.
4. The controller checks that the low air pressure
switch is open indicating no airflow. The blower
is driven towards the prestart fan speed. When the
air pressure switch closes the 15 second prepurge
time is started, and the blower is driven to the
ignition speed.
5. After the 15 second prepurge the high exhaust
backpressure switch circuit is checked to ensure
the air flow is within design parameters.
6. When the blower speed is within 200 rpm of the
ignition fan speed, a trial for ignition period of 3
seconds is initiated. The ignition spark and the gas
valves are energized.
7. The internal spark generator is de-energized after
2.7 seconds and the flame rectification system is
energized. If a flame signal is detected by the
control, a flame stabilization period of 5 seconds
at the ignition rpm of the fan. The fan is driven to
low fire for 1 minute before the boiler is released
to modulation.
8. The unit modulates between the low fire setting
and the high fire setting to maintain the desired
outlet water temp set point.
9. When the load is below the minimum firing rate of
the boiler, the boiler will continue firing and the
outlet water temperature will rise until it reaches
the set point + temperature differential. At this
point, the burner is turned off and the fan
continues to run to post purge the boiler for 15
seconds.
10. When the water temperature is reduced by the load
on the system, a heat request is again generated
and repeats the cycle.
