Specifications

Part number 550-100-090/0809
g a s -f i r e d w a t e r b o i l e r — Boiler Manual
100
Troubleshooting (continued)
Check the following:
Make sure thermostat is calling for heat and con-1.
tacts (including appropriate zone controls) are
closed. Check for 24 VAC between thermostat wire
nuts and ground.
Make sure all external limit controls are either 2.
installed (and closed) or temporarily jumpered
for testing.
Make sure that connectors to control module are 3.
securely plugged in at module and originating
control.
Gas pressures:4.
Maximum: 13” w.c. with no flow (lockup) or •
with boiler on
Minimum: 4” w.c. (for all except 5” for -299) •
for natural gas, or 4” w.c. for propane, with gas
flowing (verify during startup with boiler at
high fire)
Always check control module fuses
ALWAYS check control module fuses
before replacing control module or any
major components (blower, etc.). If one
of these fuses is blown, it can prevent
control module or other components
from operating.
Turn OFF power to boiler at external line switch.1.
Remove jacket door and jacket top panel. Rotate 2.
the swing-away control panel forward to expose
the U-Control module.
Remove and inspect the two fuses (located as shown 3.
below).
If necessary, replace the fuse:4.
Low voltage circuit fuse is 3-amp fast-blow a.
(Littelfuse 326012P).
Line voltage circuit fuse is 12-amp slow-blow b.
(Littelfuse 257003).
Do not jumper fuse or replace with any
fuse except as specified. Failure to comply
could result in severe personal injury,
death or substantial property damage.
Reinstall jacket top panel and boiler jacket door 5.
after checking the fuses.
Restore power to boiler at external line switch and 6.
verify boiler operation after completing boiler
service.
Checking temperature sensors
The boiler temperature sensors (flue, outdoor, 1.
return water and supply water) are all resistance-
type devices.
2. Figure 110 shows the correct value for the sensor
at various temperatures.
Use the resistance values at 32°F, 60°F, 70°F and 3.
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.
To check whether the control module is correctly 4.
sensing temperature, you can use a resistance de-
cade box. Connect the decade box temporarily in
place of a sensor and read the corresponding tem-
perature on the U-Control display. The temperature
should be close to the value corresponding to the
input resistance.
Sensor resistance valuesFigure 110
Sensor resistance values
Temp
(°F)
Sensor ohms
Temp
(°F)
Sensor ohms
Min Max Min Max
32
34265 37871
120
4517 4992
40
27834 30764
130
3698 4088
50
21630 23907
140
3043 3364
60
16944 18727
150
2517 2782
70
13372 14780
160
2091 2311
80
10629 11747
170
1744 1928
90
8504 9399
180
1461 1615
100
6847 7568
190
1229 1359
110
5545 6129
200
1038 1147