Table of Contents
Advertisement
23. FLAME SENSING CIRCUIT
The output of the flame sensing circuit cannot be checked directly on the S87 body. Check the
flame sensing circuit directly by checking the flame sensing current from the sensor to the S87 as
follows.
1. Connect a meter (dc microammeter scale) in series with the flame signal ground wire as
shown below. Using the Honeywell W136A Test Meter or equivalent. Disconnect the
ground wire from the S87. Connect the red (positive) meter lead to the free end of the ground
wire. Connect the black (negative) meter lead to the quick-connect ground terminal on the S87.
2. Restart the system and read the meter. The flame sensor current must be at least 1.5 uA and steady.
If the reading is less than 1.5uA or unsteady, see LOW OR UNSTEADY FLAME CURRENT
section, below.
If a flame is present at sensor and a reading of zero uA is obtained, check for a secondary
ground connection to the 25V (GND) terminal. If secondary connection exists, temporarily
remove connection and measure flame current.
1"
1/4"
to
A
good
rectifying
flame
is
achieved
with approx 1" of
sensor in a strong
blue
flame,
posi-
A lazy or weak flame
is not a good rectifying
flame. Check gas pres-
sure and gas line/
Page 28
LOW/ UNSTEADY FLAME CURRENT
If the current to the S87 flame circuit is less
than 1.5 uA or is unsteady, check the burner
flame, flame sensor location and electrical con-
nections as follows.
Electrical Connections and Shorts
Connections at the flame sensor must be clean
and tight. If wiring needs replacement, use
moisture resistant #18 wire rated for con-
tinuous duty up to 105
Flame Sensor
The flame signal is best when about 1 in. [25
mm] of flame rod is immersed in the burner
flame. A bent flame rod, bent mounting
bracket or cracked ceramic insulator can af-
fect flame signal. Replace flame sensor if nec-
essary.
Burner Flame
The flame sensor must be constantly immersed
in flame. Check burner flame conditions as
shown opposite. Observe Burner rating
plate for the correct gas pressure, and check
it with a manometer. If gas pressure is OK
check line and orifice for obstructions.
0
0
C [221
F].
GP-MSJV-BX-07A
STV-JZ Manual
RD: MAR 2009
RL: 07A - BA
Advertisement
Table of Contents
