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Part number 550-142-054/0411
GV90+ gas-fired water boiler — Boiler Manual
82
Troubleshooting (continued)
CHART 2
TSTAT CIRC & POWER lights flashing
Electrical shock hazard — Wherever you see TURN OFF POWER, follow the instructions. Failure to follow
instructions could result in severe personal injury, death or substantial property damage.
Is return water temperature sensor clamped
securely to the return pipe in the boiler?
Yes No
• Remove CIRCULATORS plug (Figure 93, page 78, Item 4)
from plug receptacle of IBC.
• Place voltmeter leads across the right-side 120 VAC N and
120 VAC H pins of the CIRCULATORS receptacle.
Does the voltmeter indicate 120 VAC?
No Yes
Is boiler internal Bypass circulator operating?
No Yes
• Test wire continuity of
circulator wire harness.
Is harness ok?
No Yes
• Check the boiler internal return pipe where it enters the
boiler sections. The TSTAT CIRC and POWER lights
will flash as long as the return water temperature is less
than 130 °F.
• Wait up to 20 minutes to give the boiler and system a
chance to respond.
Does problem persist?
No Yes
• Attach sensor to pipe with clamp provided.
• Follow return temperature sensor checking procedure
on page 76. Replace sensor if necessary.
• Retest.
• Check for stray voltage on the incoming thermostat wires.
Disconnect the two external wires connected to the boiler
thermostat wires.
• Connect a voltmeter across the two incoming wires. Close each
thermostat, zone valve and relay in the external circuit one at a
time and check the voltmeter reading across the wires. There
should NEVER be a voltage reading. If a voltage does occur
under any condition, check and correct the external wiring. (This
is a common problem when using 3-wire zone valves.)
• Once the external thermostat circuit wiring is checked and
corrected if necessary, reconnect the external thermostat
circuit wires to the boiler thermostat wires and allow the boiler
to cycle.
Did you find and correct a voltage across the two external thermostat circuit wires?
Yes No
• Boiler should now operate per the normal sequence of op-
eration (Figure 75, page 65) if wiring was corrected.
• Replace IBC (IBC).
• Retest.
• Boiler may now be operating normal-
ly. Verify against normal sequence of
operation (Figure 75, page 65).
• If boiler appears not to be heating, troubleshoot boiler
per CHART 8, page 88. If problem cannot be resolved,
replace water temperature sensor and retest. Then re-
place IBC (IBC) if sensor does not correct the problem.
• If boiler is heating, but the temperature at the return
pipe does not increase above 130 °F, there may be an
incorrectly-piped external circulator forcing water through
the boiler. Check external piping and correct.
• Reconnect circulator harness to IBC.
• Attempt to get the circulator started by giving it a sharp rap
on the end of the circulator motor (to release a possibly
locked impeller).
• If the circulator begins to operate, allow it to operate for a
few minutes to see if the problem clears.
• If problem persists, replace the Bypass circulator.
• Retest.
• Replace circulator harness.
• Retest.