Part number 550-100-131/0120
– 103 –
®
gas
-
fired
water
boiler
— 220/299/300/399
Boiler Manual
Troubleshooting
(continued)
Temp
(°F)
Sensor ohms
Temp
(°F)
Sensor ohms
Temp
(°F)
Sensor ohms
Min
Max
Min
Max
Min
Max
32
34265
37871
90
8504
9399
150
2517
2782
40
27834
30764
100
6847
7568
160
2091
2311
50
21630
23907
110
5545
6129
170
1744
1928
60
16944
18727
120
4517
4992
180
1461
1615
70
13372
14780
130
3698
4088
190
1229
1359
80
10629
11747
140
3043
3364
200
1038
1147
Figure 97
Boiler Circ fuse (control cover removed)
Figure 98
Control module fuses (control cover removed)
Figure 99
Sensor resistance valves
5. If necessary, replace one or all of the fuses:
a. Item 1 - Boiler Circ fuse is a 3-amp fast-blow (Littelfuse
0314003 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 99 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.
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.
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 97)
and remove and inspect the two (2) fuses (items 2 and 3,
Figure 98) on the control module.
Fuse
3-amp
120vac
Boiler Circ fuse
1
Line Voltage
Low Voltage 2
3
Fuse
3-amp
24VAC
Fuse
12-amp
120vac
