Owner`s manual
35
P40-R I&O Manual
IM120801
RD: NOV 2012
RL: 1B - BA
LOW/ UNSTEADY FLAME CURRENT
If the current to the S87 flame circuit is less than 1.5
µA or is unsteady, check the burner flame, flame sen-
sor location and electrical connections as follows.
Electrical Connections and Shorts
Connections at the flame sensor must be clean and
secure. If wiring needs replacement, use moisture
resistant #18 wire rated for continuous duty up to
221
0
F [105
0
C].
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 in-
sulator will affect flame signal.
Replace flame sensor if necessary.
Burner Flame
The flame sensor must be constantly immersed in
flame. Check burner flame condition as shown op-
posite. Observe burner rating plate for the correct
gas pressure, and check with a manometer. If gas
pressure is correct check line and orifice for ob-
structions.
23. FLAME SENSING CIRCUIT MODEL P40-R - HONEYWELL S87 DSI
The output of the fl ame sensing circuit cannot be checked directly on the S87 body.
Check the flame s ensing circuit directly by checking the flame sens ing 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 Tes t Meter or equivalent.
Disconnect the ground wire from the S87. C onnect the red (positive) meter lead to the
free end of the ground wire. Connect the black (negative) meter l ead to the quick-
connect ground terminal on the S87.
2. Restart the sy stem and read the meter. The flame sensor current must be at least 1.5 uA
and steady. If the r eading is less than 1.5µA
or unsteady, see LOW OR UNSTEADY
FLAME CURRENT section, below.
If a flame is pr esent at sensor and a reading of zero uA is obtained, check for a
secondary ground connection to the 24V (GND) terminal. If secondar y connection
exists, temporarily remove connection and measure flame current.
A good rectifying flame is achieved
with approx 1” of sensor in a strong
blue flame, positioned 1/4” to 1/2”
away from flame source surface.
A lazy or weak flame is not a
good rectifying flame.
Check gas pressure and gas ori-
fice for insects, and spider webs.
1.5 µA DC
minimum
and steady
1”
1/4” to 1/2”