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27
BMC and BMC-6X Installation and Operation Manual
TROUBLESHOOTING
SENSOR INPUTS
Display shows Sensor OPEN or SHORT
When OPEN, Check the sensor is connected and the wires are continuous to the BMC. Finally
follow the procedure for Incorrect Temperature or Pressure Display. When SHORT Remove the
wires from the sensor terminals. The display should change to read OPEN. If it does not, the
BMC may be damaged.
Display shows an Incorrect Temperature
Remove the wires from the sensor terminals. The display should change to read OPEN. If it
does not, the BMC may be damaged. Take an ohm reading across the detached sensor wires.
The ohm reading should correspond to the Temperature sensor Table. If it does not, the sensor
may be damaged.
CONTROL OPERATION
No Heat
• Season - Make sure that the Season is set to Winter. Check Message Display Line on page 24.
• Prove - Even though, the system relay may be energized, the BMC will not energize and stage
relays unless the Prove is shorted. Check Message Display Line on page 24.
• Shutdown - The BMC will activate stage outputs when the Shutdown terminals are short.
Check Message Display Line on page 24.
• Tstat - The BMC will activate stage outputs when the Tstat terminals are open. Check Message
Display Line on page 24.
• Sensor Fault - When the Sensor Fault is set to All Off in the startup menu (see page 16), the
System sensor fault (in all Sensor Type modes) or the Outdoor sensor fault (in Reset mode) will
de-energize all stage relays. Check the display for sensor values.
• System or Outdoor Sensor - If the System or Outdoor sensor reading was higher that the
actual temperature, the BMC might not bring any stage on. Check "Display shows an Incorrect
Temperature" section.
Too Much Heat
Check if the control has any of the following:
• Domestic Hot Water call - The BMC will raise the temperature of the system to either 200˚F or
Maximum Water Temperature on a DHW call, connected to terminals 29 and 30. Check to see
if there is a call for DHW and the length of time it lasts.
• Reset Ratio and Offset - If excessive heat occurs only in certain weather conditions, adjust the
Reset Ratio and Offset (See Understanding Operating Concept on page 5). If excessive heat
occurs year round, reduce the Offset.
• Boiler Mode Settings - The BMC will only modulate boilers their mode is set to Auto or
Standby. Check to if any boiler stage is set to Manual or On. See Mode on page 25.
• Control Settings - The Last Stage Hold will allow only the Lead boiler to stay on for an
additional number of degrees. If the setting is too high, and only the Lead boiler is on, the
system can over heat. Reduce the Last Stage Hold setting. See page 21.
Too Little Heat
Check if the control has any of the following:
• Reset Ratio and Offset - If reduced heat occurs only in certain weather conditions, adjust the
Reset Ratio and Offset (See Understanding Operating Concept on page 5). If reduced heat
occurs year round, increase the Offset.
• Setback and Day/Night Schedule - If reduced heat occurs only during specific hours, check
the Day/Night Schedule and the Setback values. Either reduce the Setback setting (See page
20).
Temperature Sensor Chart
TEMPERATURE
Value
(in Ohms)
°F °C
-30 -34 117720
-20 -29 82823
-10 -23 59076
0 -18 42683
10 -12 31215
20 -7 23089
25 -4 19939
30 -1 17264
35 2 14985
40 4 13040
45 7 11374
50 10 9944
55 13 8714
60 16 7653
70 21 5941
80 27 4649
90 32 3667
100 38 2914
110 43 2332
120 49 1879
130 54 1524
140 60 1243
150 66 1021
160 71 842
170 77 699
180 82 583
190 88 489
200 93 412
210 99 349
220 104 297
230 110 253
240 116 217
250 121 187