8
Midco
International
Inc.
8470 23
Type of
Ignitor Orifi ce
Recommended
Ignitor
Gas
Diameter Ignitor Gas Pressure
Gas Rate
NATURAL
.052 (#55Dr.)
3.5″ W.C.
6 MBH
PROPANE .042 (#58Dr.)
3.5″ W.C.
7 MBH
-
Proper operation of the fl ame sensor rod can be checked by measuring the fl ame current. With
the Electronic Control energized, a good reading should run steady 2 or more microamps.
-
When servicing, clean the Ignitor Retention Plate ports and blow out the internal air and gas
passages. Clean the Electrode Insulators and check them for hairline cracks. Also check the
electrode ends and the Ground Barrier for serious corrosion or loss of metal. Replace any defective
parts.
-
Make sure that there is no
debris in the Blast Tube that could
short out the Spark or Flame
Electrode.
-
Clean the Ignitor Gas Orifi ce in
Tee Orifi ce Fitting (see Figure 5) and
check that the orifi ce size is correct
per Table 3.
-
Check that the electrode ends
are positioned and that the gap
between the end of each electrode
and the ground barrier is spaced per
Figure 5.
-
Check that the Ignitor Air
Defl ector is at the correct angle
(45°). See Figure 4.
-
Inspect the electrode wire
insulation for cracks or worn areas,
or any contact with the burner frame.
Dampness will facilitate electrical
leakage to ground, which will cause
ignition or fl ame signal failure.
-
SPARK TEST
—Main Manual
Shut-Off Valve must be off . Place the
Ignitor Assembly on top of the burner
with the electrode ends visible and
good metal to metal contact between
the Ignitor Mounting Plate and the
burner chassis.
-
Connect the high voltage wire
to the spark electrode. Spark should be visible during 6-second trial for ignition period and arc from
the electrode end to the Ground Barrier. It should be audible and visible, though it is rather thin and
diffi cult to see in bright light.
CAUTION: Circuit has 30,000 volt open circuit potential.
-
If the spark is not audible or visible it is leaking directly to ground. Before removing electrodes,
check to make sure voltage is available by positioning the spark wire 1/8″ from the end of the
electrode.
-
Disconnect Flame Electrode
wire and switch the high voltage wire to the fl ame electrode and
repeat test for insulator leakage.
CAUTION: Do not indiscriminately change the ignitor gas orifi ce size as ignition troubles
are rarely cured in this manner. The ignitor utilizes a premixed gas/air mixture and, as the
air input is relatively fi xed, any adjustment to the gas/air ratio that might be required for a
specifi c application should be made by careful adjustment of the ignitor regulator to vary
its outlet gas pressure. Pressure adjustments must be made when the gas is fl owing. If
cleaning and electrode adjustment does not eliminate an ignition problem, further checks are
required. Refer to Trouble Chart.
__________________________________________
The valve is a single function on-off type with automatic closing on current failure. Replace
entire valve if valve fails to open when power is applied or if leakage is defected on standby.
__________________________________________
Table 3 1 -
Ignitor Firing Rate
VIII Ignitor &
Regulator
Assembly
Continued
Figure 5 -
Ignitor and Flame Sensor Assembly
IGNITOR
SPIDER
SENSE
ROD
.25
GROUND
BARRIER
SPARK ELECTRODE
POSITION ELECTRODES TO CENTER
HOLE ON RETENTION PLATE
IGNITOR
GAS
PRESSURE
IGNITOR REGULATOR
IGNITOR
MOUNTING PLATE
INSULATOR
INSULATOR
CLAMP
CLAMP SCREWS
1/8 TO 5/32 GAP
1/8 TO 5/32 GAP
IGNITOR GAS ORIFICE
(HIDDEN: SIDE TAP OF TEE)
TEE ORIFICE FITTING
IGNITOR
GAS LINE
IGNITOR TIP
RETENTION PLATE
TEST TAP
IX Main
Automatic Valve
Service
