Tank Probe - A.O. Smith 100 Series Service Handbook

DISPLAYED MESSAGE/CONDITION/INDICATES

Tank Probe

The Control System has detected an open or shorted
Remote (Tank/Loop) Temperature Probe circuit when the
Remote Temperature Probe, or optional Quad Thermistor
Probe, is configured as the Controlling Probe. See The
Controlling Probe on page 7 and the SW1 dipswitch
information on page 23.
If the Remote Temperature Probe or the optional Quad
Thermistor Probe is not configured as the Controlling
Probe and the Remote Temperature Probe circuit is open
or shorted, the boiler will continue to operate. In this
condition the UIM's LCD display will show dashed lines
(-----) in place of the Tank temperature reading when
the Remote Temperature Probe circuit is open and will
display the word "Short" when the circuit is shorted. See
the illustrations below.
Out let
- I nlet
= D el ta T
Ta nk
O utlet
- I nl et
= D elt a T
Tank
Installation Notes:
Each VF Boiler is fired and the optimal combustion
is set before leaving the factory. The Inlet Probe is
configured as the Controlling Probe at the factory during
this process. The Inlet Probe MUST NOT be configured
as the Controlling Probe when the boiler is installed. All
VF Boilers are supplied from the factory with a Remote
Temperature Probe to be installed in a storage tank
on domestic water applications or in the return loop in
hydronic heating systems. The Remote Temperature
Probe, or optional Quad Thermistor Probe MUST BE
configured as the Controlling Probe on all applications,
see the The Controlling Probe on page 7 and the SW1
dipswitch information on page 23.
Important Service Reminder:
When performing any troubleshooting steps outlined in
this manual always consider the wiring and connectors
between components. Perform a close visual inspection
of all wiring and connectors to a given component before
replacing any electrical part or component.
1 40 ° F
1 25 ° F
15 °F <2 0
---- --
1 4 0° F
1 2 5° F
1 5°F <2 0
Sh or t
Servicing should only be performed by a Qualified Service Agent
CHECK/REPAIR
• Check the plug/socket connection at the MCB J9
Socket, see MCB - Section E on page 24. Ensure the
plug/socket pins are in good condition and making
good contact - repair/replace anything worn or
damaged.
• Ensure the wiring between the MCB J9 Socket and
the Remote Temperature Probe or optional Quad
Thermistor Probe (see pages 15 and 16) are not pinched
and are continuous - repair/replace anything worn or
damaged. Ensure wiring ran in field installed conduit
between the boiler and the Remote Temperature
Probe is continuous.
• Turn power off to the boiler. Unplug the MCB J9
wiring harness plug. Measure and record resistance
between pins 3 and 4 of the J9 plug. Measurement
may also be taken at the probe if the wiring is
disconnected.
• If the measured resistance is less than 317 ohms
or greater than 177,000 ohms - replace the Remote
Temperature Probe.
• If the measured resistance is less than 317 ohms
or greater than 177,000 ohms - replace the Quad
Thermistor Probe or connect the wiring from the
boiler's MCB J9 socket to an unused thermistor
circuit in the Quad Thermistor Probe if available.
Service Note:
Resistance from any factory supplied/installed
temperature probe is shown in Table 3 on page 16.
• Call the toll free support phone number on the back
cover of this manual for further assistance if the
problem has not been corrected after performing the
procedures outlined here.
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