Williamson-Thermoflo GWC-070 Manual page 81

GWC -
gas fired water boiler
Troubleshooting
CHART 3
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.
• This is a LOCKOUT condition. The return water temperature
sensor has signaled a temperature higher than 240 °F, but the
boiler limit circuit is closed (indicating that the limit control circuit
• TURN OFF POWER to boiler at 120 VAC service switch.
• Remove CONTROL CIRCUIT plug from IBC receptacle (Fig-
ure 89, page 76, Item 5).
• Replace control wiring harness.
• Retest.
• Replace water temp sensor.
• Retest.
• Close the external manual gas valve.
• Remove one wire from the limit control space
connector.
• Set a thermostat to call for heat. Then turn on
power to the boiler at the 120 VAC service switch.
• The boiler system circulator should come on and
the IBC should try to cycle the boiler.
• Allow the boiler circulator to run to cool off boiler
and system water.
• After the boiler and system water have cooled,
turn off power at the 120 VAC service switch and
open the external manual gas valve.
Part number 550-142-056/0411
— Boiler Manual
(continued)
LIMIT & POWER lights flashing
Does the ohmmeter indicate a shorted wire harness (zero ohms)?
Yes
did not catch the over-temperature condition). This is probably
an indication of a failure of the boiler limit control and possibly
the block temperature switch as well.
• Remove a wire from one of the limit control spade connec-
tors.
• Connect an ohmmeter across the left and right pins on the
center row of the limit circuit harness.
• Reconnect CONTROL CIRCUIT plug to IBC.
• Remove WATER TEMP SENSOR plug from IBC receptacle
(Figure 89, page 76, Item 6).
• Connect an ohmmeter across the plug pins to check the sen-
sor resistance.
Does the ohmmeter indicate a shorted sensor (zero ohms)?
Yes
Is boiler hot?
Yes
• Set limit control knob to its minimum setting. Replace wire to
limit control spade connector.
• Set a thermostat to call for heat.
• Turn on power at 120 VAC service switch.
• IBC should cycle boiler on and begin heating.
• The limit control should shut off the gas valve when the
temperature at the boiler pressure/temperature gauge has
reached no more than about 20 °F higher than the limit
switch setting.
Does limit control shut off gas correctly?
Yes
• Replace IBC.
• Retest.
No
No
No
No
• Replace limit control and
block temperature switch.
• Retest.
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