Check The Following; Checking Temperature Sensors - Weil-McLain Ultra Commercial Installation And Start-Up Manual

COMMERCIAL GAS
Troubleshooting

Check the following:

1. Make sure thermostat is calling for heat and con-
tacts (including appropriate zone controls) are
closed. Check for 24 VAC between thermostat wire
nuts and ground.
2. Make sure all external limit controls are either
installed (and closed) or temporarily jumpered
for testing.
3. Make sure that connectors to control module are
securely plugged in at module and originating
control.
4. Gas pressures as specified on
or page 50 (propane).
Always check control module fuses
1. Turn OFF power to boiler at external line switch.
2. Remove jacket door and jacket top panel. Rotate
the swing-away control panel forward to expose the
U-Control module and Expansion module.
3. Remove and inspect the two U-Control fuses and
the Expansion module fuse (located as shown
below).
4. If necessary, replace the fuse:
a. Low voltage circuit fuses on U-Control and
Expansion module are 3-amp fast-blow
(Littelfuse 326012P).
84
-
FIRED WATER BOILER
(continued)
page 50 (natural gas)
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.
— Boiler Manual
b. Line voltage circuit fuse is 12-amp slow-blow
(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.
5. Reinstall jacket top panel and boiler jacket door
after checking the fuses.
6. Restore power to boiler at external line switch and
verify boiler operation after completing boiler
service.

Checking temperature sensors

1. The boiler temperature sensors (flue, outdoor,
boiler out, boiler in, heat exchanger and system)
are all resistance-type devices.
2. Figure 78 shows the correct value for the sensor at
various temperatures.
3. Use the resistance values at 32°F, 60°F, 70°F and
212°F to measure the sensor resistance at known
temperatures (freezing point, room temperature
and sea level boiling point). For freezing point
and boiling point, insert the sensor in water at that
temperature. Use an ohmmeter to read resistance
value.
4. To check whether the control module is correctly
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 values
Sensor resistance values
Sensor ohms
Temp
(°F)
Min
32 34265
40 27834
50 21630
60
70 13372
80
90
8504
100 6847
110 5545
Sensor ohms
Temp
(°F)
Max Min
37871 120 4517
30764 130 4088
140 3043 3364
18727 150 2517 2782
14780 160 2311
11747 170 1744
180
1461 1615
7568 190
200 1038 1147
Part number 550-100-086/0809
Max