Service manual

36
Main Burner
When all pilot flames are established, a flame
rectification circuit is completed between the
sensor and the burner ground. The flame
sensing circuit in the ignition module detects the
flame current, shuts off the spark generator and
energizes the combination valve operator. Once
all pilots are lit the main gas valve opens and
matches gas input to the available air. As the
fans ramp up gas input is adjusted accordingly.
On the lock out ignition module, the flame
current also holds the safety lockout timer in the
reset operating condition. When the call for heat
ends, both valve operators are de-energized,
and both valves in the gas control close.
Normal Operation
Modulation is controlled from the Boiler
Temperature Controller. The modulating fans
are equipped with electrically commutated DC
motors which respond to a PWM signal.
The control provided with the Modulating
MicoFlame allows remote control with an analog
signal of 4-20mA or 2-10VDC.
Demand Satisfied
The BTC 1 senses that the boiler target
temperature was reached and de-energizes the
stage contact.
Control Alarms
High limit or low water flow will de-energize all
gas valves, and the blower. Condition indicators
are visible on the control panel. Each
burner/blower set is provided with its own air
pressure switch. If a low air pressure condition is
present, power will not be supplied to the ignition
module. The blower will remain on and the air
indicator will remain on for as long as there is a
call for heat.
11 PILOT AND MAIN BURNER
FLAMES
11.1 MAIN BURNER
The main burner, Figure 25 should display the
following characteristics;
• Acceptable CO and CO
2
levels for
complete combustion
• Light off smoothly
• Reasonably quiet while running
• Stable flame with minimum of lifting
• Blue flame with natural gas, yellow tips
with propane gas
Figure 25 - Burner
If burner characteristics do not match the above,
check for proper air box pressure. Look for
accumulation of lint and other foreign material at
fan air inlets.