Checking Temperature Sensors - Weil-McLain Evergreen 220 User Manual

™ GAS
Troubleshooting
Check Control fuses
ALWAYS check control fuses before replacing
control or any major components (blower, etc.). If
one of these fuses is blown, it can prevent control
or other components from operating.
1. Turn OFF power to boiler at external line switch. Then remove
the jacket door.
2. Remove four (4) screws holding control tray cover in place.
3. Remove control tray cover to access the fuses.
4. Remove and inspect the one (1) fuse (item 1, Figure 94)
and remove and inspect the two (2) fuses (items 2 and 3,
Figure 95) on the control module.
Boiler Circ fuse (control cover removed)
Control module fuses (control cover removed)
Line Voltage
Part number 550-100-131/0715
-
FIRED WATER BOILER
(continued)
Fuse
3-amp
1
120vac
Boiler Circ fuse
Low Voltage 2
Fuse
3-amp
24VAC
Fuse
12-amp
120vac
3
— Boiler Manual
5. If necessary, replace one or all of the fuses:
a. Item 1 - Boiler Circ fuse is a 3-amp fast-blow (Littelfuse
0315003 MXP or Bussman ABC-3-R).
b. Item 2 - Low voltage circuit fuse is a 3-amp fast-blow
(Littelfuse 0287003).
c. Item 3 - Line voltage circuit fuse is a 12-amp fast-blow
(Littelfuse 0314012 MXP or Bussman ABC-12-R).
Do not jumper either fuse or replace with any fuse
except as specified. Failure to comply could result in
severe personal injury, death or substantial property
damage.
6. Reinstall control tray cover.

Checking temperature sensors

1. The boiler temperature sensors (flue, outdoor, return wa-
ter, supply water and system temperature sensors) are all
resistance-type devices. Figure 96 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.
Sensor resistance valves
Temp Sensor ohms Temp
(°F)
Min Max
32 34265 37871
40 27834 30764
50 21630 23907
60 16944 18727
70 13372 14780
80 10629 11747
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.
3. To check whether the Control is correctly sensing tem-
perature, 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.
Sensor ohms Temp Sensor ohms
(°F) (°F)
Min Max
90 8504 9399 150 2517
100 6847 7568 160 2091
110 5545 6129 170 1744
120 4517 4992 180 1461
130 3698 4088 190 1229
140 3043 3364 200 1038
Min Max
2782
2311
1928
1615
1359
1147
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