No Flow - A.O. Smith 100 Series Service Handbook

DISPLAYED MESSAGE/CONDITION/INDICATES

No Flow

Pump IS NOT Running
(If the pump is running see "No Flow - Pump Is Running" on the
following page)
The Control System has detected the normally open
contacts on factory mounted Flow Switch are not closing
or are not remaining closed after the pump is energized.
See Figure 2 on page 8 for location of Flow Switch on the
back of the boiler.
Service Notes:
The power should be on with a call for heat present when
performing the voltage checks described in the right
column. The boiler's control system may continue to lock
out after the allotted time to prove the pump is operating
properly via the flow switch has expired. See Resetting
Control System Lock Outs on page 48. Reset Control
System lock out conditions as necessary to conduct the
diagnostic procedures listed here.
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.
54 Servicing should only be performed by a Qualified Service Agent
CHECK/REPAIR
Field Installed Boiler Circulation Pump
• Check for power at the pump motor wiring/terminals.
If the pump is being supplied with the correct voltage
(see field installed pump rating plate) but will not start
- replace/repair the pump.
• If the field installed pump is equipped with a dual
(multiple) voltage motor, ensure the pump motor
wiring has been correctly configured for the voltage
supplied, see field installed pump rating plate and
manufacturer's instructions for voltage conversions.
• If power is not present - ensure all field installed
pump controls, wiring, connectors, and relays or
starters are functioning correctly. Make necessary
repairs to restore power to pump, see Field Supplied
Boiler Circulation Pumps on page 30.
• If a field installed pump receives power from the
boiler's pump relay and/or PDB circuit board check
fuse and pump relay as outlined in the steps listed for
models with factory installed pumps below.
Factory Installed Boiler Circulation Pump
• Check for 120 VAC at the pump motor wiring/
terminals. If the pump is being supplied with 120 VAC
but will not start - replace/repair pump.
• Check F2 fuse on PDB - replace fuse if blown, see
page 30.
• Check for 120 VAC at MCB J2 socket pins 1 & 2
supplying power to the pump relay coil, see page 22.
• Check for 120 VAC at pump relay coil terminals.
If correct voltage is not present check all wiring
between MCB J2 socket pins 1 & 2 and the pump
relay. Ensure the MCB J2 plug/socket pins are in
good condition and making good contact - repair/
replace anything worn or damaged.
• Ensure pump relay N.O. (normally open) contacts are
closing with 120 VAC supplied to the pump relay coil.
If contacts do not close - replace pump relay.
• Check for 120 VAC hot to the N. O. contact terminal
of the pump relay at TB1 terminal 1 on the PDB
(page 29). Check to ground/neutral.
• Check for 120 VAC hot return from the Common
contact terminal of the pump relay at TB1 terminal 3
on the PDB (page 29). Check to ground/neutral.
• Check for 120 VAC to the pump motor between TB1
terminals 4 & 5 on the PDB (page 29).
• Ensure hot/neutral wires from pump are in good
condition and properly connected to TB1 terminals 4
& 5 on the PDB (page 29).
• 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.