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Troubleshooting (continued)
Check ECO control fuses
ALWAYS check ECO control fuses before replacing ECO
control or any major components (blower, etc.). If one of
these fuses is blown, it can prevent ECO control 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 95.
3. Remove and inspect the two fuses (items 1 and 2, Figure 95).
4. If necessary, replace one or both of the fuses:
a. Low voltage circuit fuse is 3-amp fast-blow (Littelfuse 326012P).
b. Line voltage circuit fuse is 12-amp slow-blow (Littelfuse 257003).
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.
Checking temperature sensors
1. The boiler temperature sensors (flue, outdoor, return water and supply
water) are all resistance-type devices. Figure 94 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 resis-
tance value.
3. To check whether the ECO control is correctly sensing temperature,
you can use a resistance decade box. Connect the decade box tempo-
rarily in place of a sensor and read the corresponding temperature on
the ECO control display. The temperature should be close to the value
corresponding to the input resistance.
&IGURE
Sensor resistance values
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
Part number 550-142-122/0513
91
TM
GAS-FIRED WATER BOILER — Boiler Manual
&IGURE Control fuses
1
2
Line Voltage
Low
Voltage
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