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Part number 550-142-054/0411
GV90+ gas-fired water boiler — Boiler Manual
88
CHART 8
Insufficient heat or no heat to system (POWER light on steady)
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.
Troubleshooting (continued)
• Has it been at least 5 minutes since setting thermostat to
call for heat? If not, wait 5 minutes. Is system heating?
• Is thermostat set to call for heat? Remove thermostat
wires at boiler and check continuity across the two wires. If
circuit isn't closed, check external thermostat (zone valve,
relay, etc.) wiring. Correct problems and retry.
• Reconnect external thermostat wiring at boiler.
Is thermostat circuit closed (continuity across wires)?
No Yes
Is boiler System circulator operating?
No Yes
• Wait 5 minutes.
Is FLAME light on?
No Yes
• If you have sufficient heat — boiler should follow normal
operating sequence (Figure 75, page 65).
• If you have less than sufficient heat —
Is vent or combustion air piping free of blockage?
No Yes
• Wait for boiler water to cool to temperature 20 to 30 °F
lower than temperature set on limit switch.
Are limit switch contacts closed?
No Yes
Are all red lights off?
No Yes
• Wait 30 seconds.
Are all red lights
off?
No Yes
• Wait for cast iron
block to cool to room
temperature.
Are block switch
contacts closed?
No Yes
• Check across thermal fuse
leads with continuity checker.
Is circuit closed?
No Yes
• Check across limit
switch contacts with
continuity checker.
Are contacts closed?
Yes No
• Replace IBC.
• Retest.
• Replace IBC.
• Retest.
• Correct conditions and
recheck operation. See
sequence of operation, Fig-
ure 75, page 65.
• Repair/replace circula-
tor. Retest.
• Repair/replace wiring.
Retest.
• Contact your Weil-
McLain sales represen-
tative.
• Replace
switch.
• Retest.
• Replace
thermal fuse.
• Retest.
• Replace IBC.
• Retest.
• Replace limit switch.
• Retest.
• Excessive block temperature has been reduced to safe op-
erating level. Check for low water level or mineral deposits
in sections. Correct before proceeding.
• Restart boiler and check sequence of operation (Fig-
ure 75, page 65).
• Boiler water temperature exceeded setting on limit switch
with thermostat calling for heat. Boiler is OK. (See se-
quence of operation, Figure 75, page 65)
• Also check operation of setting on limit switch (should be
above 140°F.).
• Check block switch on top of
boiler with continuity checker.
Are contacts closed?
No Yes
• Boiler is in standby.
• Set thermostat to call for heat
and recheck operation.
• Verify sequence of operation,
Figure 75, page 65.
• Remove system circulator harness plug from CIR-
CULATORS plug receptacle (long harness) (see
Figure 93, page 78, Item 4). Check with voltmeter
across left-side 120 VAC N and 120 VAC H pins of
receptacle.
Does voltmeter show 120 VAC across pins?
No Yes