Weil-McLain Aqua Balance WMB-155 Manual page 87

W
TM
AquaBalance
34 Troubleshooting
Check flame signal
1. Navigate to Diagnostics/Inputs on the control display (see
pages 60 to 64 for navigation instructions.
2. The flame signal value must be at least 25 on low fire. The
flame signal value must be at least 255 on high fire, reading
at times 10 equals microamps of flame signal. If the flame
signal drops below this level, the control will attempt to cor-
rect by increasing the blower speed to increase flame signal.
3. A low flame signal may indicate a fouled ignitor or damaged
ignitor cable insulation.
a. See "Inspect ignition electrode," page 107 to remove
and inspect the ignitor.
b. If required, clean the ignitor and flame rod as in-
structed, see page 107.
c. If cleaning the ignitor does not improve, ground wiring
is in good condition, and ground continuity is satisfac-
tory, replace the ignitor.
4. If flame signal still remains low:
a. Inspect the vent and air piping.
b. Check combustion values.
c. Then inspect the heat exchanger, following the proce-
dures given in this manual for inspecting and clean-
ing of the heat exchanger cover plate and other boiler
components (starting on page 107).
d. Clean the heat exchanger as described in this manual if
necessary, see page 110.
Check control fuse
ALWAYS check circuit fuses before replacing
control or any major components (blower,
etc.). If a fuse is blown, it can prevent the con-
trol or other components from operating.
1. Turn OFF power to boiler at external line switch. Then
remove the jacket door.
2. Locate fuses using Figure 110 and Figure 111.
3. Remove and inspect the fuses (Item a, Figure 110 or Item
b, Figure 111).
4. If necessary, replace the fuses:
a. Control circuit fuse is a 250 VAC 3.15-amp rated
fuse. (Littelfuse 326012P)
b. Thermostat-relay circuit fuse is a 250 Volt 630mA rated
fuse. (Littelfuse 071-852 Type 5 x 20mm).
Do not jumper fuses or replace with any fuse
except as specified. Failure to comply could result
in severe personal injury, death or substantial
property damage.
Checking temperature sensors
1. The boiler temperature sensors (flue, outdoor, return
water and supply water) are all resistance-type devices.
Figure 112 shows the correct value for the sensor at various
temperatures. For dual sensors, the temperature difference
between the sensors must be no more than 10 °F. (Supply
outlet 200 sensor).
2. Use the resistance values at 32°F, 60°F, 70°F and 212°F to
measure the sensor resistance at known temperatures (ice
point, room temperature and sea level boiling point). For
ice point and boiling point, insert the sensor in water at
that temperature. Use an ohmmeter to read resistance value.
Part number 550-100-305/0118
M -
ALL OUNT GAS FIRED WATER BOILER
(continued)
—
Boiler Manual
Figure 110 Control circuit fuse location
Fuse located on rear of circuit board
Figure 111 Thermostat-relay circuit fuse location
Installer/homeowner note,
in case of an "open circuit"
of the Thermostat-relay
fuse the boiler can run in
DHW mode but NOT in
Central Heating mode.
b
3. To check whether the control is correctly sensing temperature,
you can use a resistance decade box. Connect the decade box
temporarily in place of a sensor and read the corresponding
temperature on the control display. The temperature should
be close to the value corresponding to the input resistance.
Figure 112 Sensor resistances values
Temp Temp
Sensor ohms
(°F) (°F)
Min Max
32 31530 33480 100
40 25792 27388 110
50 19258 20450 120
60 15218 16160 130
70 11577 12293 140
80 8891 9441 150
90 7185 7629 160
a
Temp
Sensor ohms Sensor ohms
(°F)
Min Max Min
5608 5954 170 1344
4590 4874 180 1143
3636 3860 190 945
3011 3197 200 810
2417 2567 212 657
1954 2074 - -
1644 1746 - -
Max
1428
1213
1003
860
697
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