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HONEYWELL
L7148F TROUBLE
SHOOTING
GUIDE
Start
Boiler is cold.
Boiler is not reaching proper temperature
or will not tum on.
4,
Check:
L7t 48F Diagnostic LED =ON"?
I
Yes
Set room thermostat
lO°above
room
/
temperature.
Set boiler 10° (or more) above current
water temperature.
Boiler turns on?
Yes
i
Check Circulator Pump, running?
I
Yes
I
Boiler shuts off at high limit setting?
I
No
!
Boiler shuts off above high limit setting?
t
No (Below HL)
4,
Check L7148F diagnostic
LED Flashing?
I
No
4,
Check:
Temperature/Pressure
gauge accuracy.
Thermo Well tocated per boiler OEM
instructions.
--
No--
]
No
Check for 12BY at LIX,
L2X.
Check for 24V at R C
I
___
Short terminals W-R (T-TW)
___
on L7148.
No
Boiler starts?
I
No
÷
Check:
_-_
L7148F Diagnostic LED, flashing?
I
No
÷
Check:
L7148F in reset mode (wait 5 minutes
for control to reset).
Vent damper apen?
Turn power "ON".
Check all wiring connections.
Replace transformer as appropriate.
Thermostat cr Thermostat
widng problem.
Check system per instructions
provided
with thermostat.
Two Blinks:
replace sensor.
Check sensor connections.
If good,
_
Three or four blinks:
Yes
Internal error, replace L71 48F control.
I
Check for 24V, at 81, B2?
I
I
J
,
--
Yes
4,
L7148F is OK, check ignition and gas
valve system as described in literature
provided with those products
t
No
Check vent damper cable and
I_
t
connections.
Replace vent damper cable or damper
as appropriate.
_r
I 120vacatC1,C27
L
/
i
Y_s
4,
L7148F is OK
Check other system components:
Circulators, Zone Valves
Check:
Temperature/Pressure
gauge
accuracy
Sensor fully inserted into well
Thermo Well in good condition.
Thermo Well located per boiler OEM
recommendations.
No
Yes
Yes
L_
Check room thermostat,
ts it still set at
10° above current room temperature?
7'
Yes
_t
No
Two blinks, replace sensor,
Three or four blinks, replace control.
Replace L7148F.
Control failure, incapable of self
diagnostics.
_r
I Reset thermostat and repeat voltage check
I
i
I
34
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