50
Part Number
550-110-290/0219
CGt
GAS-FIRED WATER BOILER — Series 2 —
Boiler Manual
Troubleshooting — control module lights
(cont.)
12c
CHART 2 ––
TSTAT CIRC
& POWER light flashing
–– Usually indicates 48VAC on thermostat circuit (stray voltage) ––
120
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.
• If no voltage is found under any condition of the
external thermostat circuit, connect the two boiler
thermostat connection leads together (or jumper the
boiler aquastat T-T terminals).
• Turn off power to the boiler for 1 minute.
• Turn on power and allow boiler to cycle.
Does the
TSTAT
and
POWER
lights still flash?
No
Yes
• Disconnect the two external wires connected to the boiler
thermostat leads (two (2) black low voltage leads in J-box).
• Connect a voltmeter across these two (2) 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
operation (Figure 27, page 34).
• Leave external boiler thermostat connection wires
disconnected from boiler.
• Troubleshoot the external thermostat circuit until you
find the source of the stray voltage. (Pay close atten-
tion to the wiring connections to 3-wire zone valves.)
• Correct the problem and repeat the voltmeter test
above, verifying there is no longer a voltage reading
under any condition in the external thermostat circuit.
• An isolating relay may be required.
Replace control module.
Retest.