Landa NG-3000, Operator'S Manual

Page: 22 / 30

22
Maintenance
Burner Troubleshooting
Millivolt Check
This machine has a thermopile self-powered combina -
tion gas control. Before checking the millivolt system,
the following operations should be performed and
observations made:
1. Inspect system for proper wiring.
2. The switch leads and all wire connections should
be cleaned and tightened to eliminate all
unnecessary resistance.
3. Clean and/or adjust pilot for maximum flame
impingement on the thermopile.
4. If pilot will not remain lit when gas cock dial is
released, check automatic pilot (Step D).
The millivolt system and individual components may be
checked with a DC millivolt meter having a 0-1000MV
range. Conduct each check as shown in the chart
below by connecting the meter test leads to terminals
as indicated. All readings are closed circuit.
Troubleshooting Gas Valve
A. Complete Millivolt System Check
(“A” Reading = Switch contacts CLOSED - Gas
Cock Dial “ON” - Main burner should come ON).
5. If the reading is more than 100 millivolts and the
automatic valve still does not come on, replace the
automatic valve operator.
6. If the closed circuit reading (“A” Reading) is less
than 100 millivolts, determine cause for low
reading - proceed as follows:
B. Thermopile Output Reading Check
(“B” Reading = Switch contacts OPEN - Main
burner OFF).
If the minimum 250 millivolt reading is not
obtainable, readjust pilot for maximum millivolt
output. If millivolt reading is still below minimum
specified, replace thermopile.
C. System Resistance Check
(“C” Reading = Switch contacts CLOSED - Gas
Cock “ON” - Main burner should be ON)
If the “C” Reading is more than that specified for
the system being checked, this indicates the
resistance in the system is excessive and must
be reduced. To correct:
a. Clean and tighten switch leads and
connections.
b. Shorten switch lead wires and/or replace
with heavier gauge wire.
c. Cycle switch rapidly to clean contacts.
D. Automatic Pilot Dropout Check
1. Hold gas cock dial depressed in pilot position until
maximum output is observed. Then extinguish pilot
and observe meter.
2. Dropout of automatic pilot magnet (sound should
be audible) should occur between 120 millivolts
and 30 millivolts. If dropout occurs outside these
limits, change the automatic pilot magnet
assembly.
TH3
TH/PP1
PP2
Landa NG 3000 Operator’s Manual 8.913-942.0 - E
Check
Test
To Test
Connect
Meter
Leads to
Terminals
Switch
Flow &
Burner
Contacts
Meter
Reading
Should
Be:
A
Complete
System
2 & 3 Closed
100 MV or
More
B
Thermopile
Output
1 & 2 Open
Greater
than 250
C
System
Resistance
1 & 3 Closed
Less than
35
D
Auto/Pilot
Dropout
1 & 2 Open
Between
120-30 MV