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Updated: Feb 10, 2023
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Weil-McLain boiler error codes

The manufacturer of products Weil-Mclain is a subdivision of the Marley-Wylain Company, which is a leader in North America due to the production of heating systems since the 1881. Weil-Mclain products differ by high technologies and modern materials of their production. They are securely and functionally designed with consideration of aesthetics and safety principles. Below you will find a table with Weil-Mclain error codes.

Weil-McLain SlimFitn boiler error codes

Error code Description Error code Description
2 Waiting for safety data verification 91 Inlet sensor fault
3 to 46 Internal Fault 92 Outlet Sensor fault
47 Flame Rode to ground leakage 94 Header sensor fault
49 24 VAC voltage low/high 95 Stack sensor fault
53 AC inputs phase reversed 96 Outdoor sensor fault
63 LCI OFF 105 Rame detected out of sequence
64 Pll OFF 106 Rame lost in main flame establishing period
67 ILK OFF 107 Flame lost early in run
79 Outlet High Limit 108 Rame lost in run
81 Delta T limit 109 Ignition failed
82 Stack Limit 122 to 132 Rate proving vaults
85 Inlet/Outlet inversion limit 172-178 Internal Control Relay fault
88 Outlet T-Rise limit 184-250 Parameter setting fault
25 Lead lag operation switch was turned off 183-203 Lead lag parameter errors
26 Lead lag operation switch was turned on 204-213 Lead lag operation errors
29 Burner switch turned off 268 CH 4mA water temperature setting invalid
30 Burner switch turned on 269 CH 20 mA water temperature setting was invalid
44-70 System operation faults 272-360 Abnormal Recycle
74-81 Fan parameter errors 361-382 Internal errors
84-114 Modulation parameter errors 460 LCI lost in run
115-130 Modulation operation faults 461-463 Abnormal recycle: demand lost in run
131-145 and 150-156 CH parameter errors 467-500 Internal data faults
146-149 and 179-182 CH operation error 540-559 Delta T errors
157-170 DHW Parameter errors 560-575 T rise errors
171-187 DHW operation errors 576-581 Pump errors

Weil-McLain Ultra boiler error codes

Message displayed Condition causing automatic reset Reset action
Display fault Display communications out for 30 seconds Resets automatically when communication is re-established
Automatic reset limit open Set if auto reset limit open
Supply water temperature high Set if the supply water temperature is higher than 200 °F Reset after heat exchanger oudet temperature is less than burner on temperature Reset with manual reset on display
Return water temperature high (heat exchanger input) Set if the return water temperature is higher than 200 °F
Return water temperature greater than supply water temperature Set if heat exchanger inlet temperature is higher than the heat exchanger outlet temperature +10 F Reset when return temperature minus 9 °F is less than supply temperature or Reset with manual reset on display
Supply water rising too fast Set if supply water temperature rises faster than 2 °F per second Reset after 1 minute delay Reset with manual reset on display
Supply greater than return by 58 °F Set if current heat exchanger outlet temperature is greater than the heat exchanger inlet temperature + 58 T
Temperature sensors Supply sensor open or shorted Return sensor open or shorted. Set if flue sensor not balanced (more than 10 °F difference between sensors) Set if heat exchanger outlet sensor not balanced (more than 10 °F difference between sensors) Reset if sensors balance
Flue temperature high Set if flue temperature over 210 °F Reset after 1.5 minute delay
LWCO fault Set if 1WCO open goes to manual reset lockout if open more than 1 second Reset when closed

Weil-McLain WM97+ boiler error codes

Display Diagnostics Action
Nothing shown on display screen and boiler will not respond to call for heat Check wiring for short circuit or incorrect wiring. Correct wiring per wiring diagram including connection of transformer to the control module.
Check 3 – amp low voltage fuse on control module Replace fuse with proper part found in replacement part section of this manual. If fuse blows again recheck wiring per diagram.
Check transformer connection to the control module per wiring diagram. Check for 24V output of transformer. Replace transformer if it is is receiving 120Vac, but not outputting 24Vac.
Nothing is shown in display screen and no other boiler components are operating Check service switch and/ or circuit breaker to boiler turned is on. Turn on service switch to power boiler.
Is there 120 Volts at the service switch? Troubleshoot and correct the power supply to the service switch.
Is the WM97+’s ON/ OFF POWER SWITCH located on top of the boiler Turn the WM97+’s power switch to ON.
Check for 120 volts at the line voltage terminal block located inside the top left electrical compartment Correct wiring inside the control pod using the wiring diagram in this manual.
Inspect 12 – amp fuse. Replace if necessary. Replace the fuse with proper part found in the replacement part section of this manual. If fuse blows again recheck wiring per diagram.
Nothing is shown on display screen, but boiler is operating Check for loose connections and proper pin alignment/ engagement on the control module’s plug P9 and the back of the display circuit board. Check for continuity on the wire harness from the display to the control module. See repair parts section for proper replacement part.
Cycle power off and on using boiler power switch and check for operation. Replace with new display module. See repair parts section for proper replacement part.
TEMP RISE TOO QUICKLY Automatically resets after 1 minute delay or using manual reset on display. Verify water pipe is installed correctly per instructions in this manual.
Manual reset is necessary after 5 automatic resets have occurred during the same Priority heat demand. Reset using manual reset screen on display Verify proper circulator and speed for boiler size and system requirements.
See message displayed TEMPERATURE SENSOR and follow procedure for loose connections.
SUPPLY 58F> RETURN Automatically resets after 30 second delay or using manual reset on display. Verify water pipe is installed correctly per instructions in this manual.
Verify proper circulator and speed for boiler size and system requirements.
See message displayed TEMPERATURE SENSOR and follow procedure for loose connections.
RETURN > SUPPLY Automatically resets when condition no longer exists. Verify proper flow direction of the boiler circulator. This circulator must be installed to push water through the boiler’s return pipe. Verify proper boiler circulator speed setting in the control module.
TEMPERATURE SENSOR Will automatically reset if the condition clears Check all the temperature readings of the boiler on the DIAGNOSTICS – TEMPERATURES menu to determine if any sensors are currenty displayed as SHORT or OPEN. Compare this to the boiler temperatures recorded in the DIAGNOSTICS – ERRORS – LOCKOUT HISTORY # – TEMPERATURES during the last several lockout conditions. If the resistance values are incorrect replace the temperature sensor. Refer to repair parts section for proper part number. OUTDOOR TEMP is the optional outdoor air temperature sensor. If this are not being used they will always be shown as OPEN. This is normal unless the sensors were installed.
Check wire harness for loose connections and pin engagement at sensor connection, chassis mount connection through control housing, and the control module. Unplug connection at sensor and at control module and check continuity between ends.
If problem persists after checking items above replace control module. Refer to repair parts section for kit number.
Automatically resets when sensors are within 10°F. Follow procedure for above for SHORT and OPEN sensor conditions to properly diagnose sensor. If measured resistance values of sensors convert to temperatures seperated by more than 10°F replace the sensor.
FLUE TEMP TOO HIGH Automatic reset occurs if temperature drops below 216°F for 2.5 minutes. Manual reset is required if the temperature rises above 225°F. Reset using manual reset screen on display Follow procedure for above for SHORT and OPEN sensor conditions to properly diagnose sensor. In addition inspect heat exchanger combustion chamber and flueways for abnormal wear or buildup. Inspect vent system for abnormal wear or damage. Contact Weil – McLain Technical Support.
DISPLAY COMM Automatically resets when communication is re – established. Check for a loose connection at the molex plug on the control and connection on the back of the display.
LIMIT OPEN Automatic external limit will reset 2.5 minutes after external limit device closes. Manual limit fault must be reset by choosing Reset Lockout on the display. Is there an external safety device connected? If yes, trouble shoot the external limit to determine and correct the cause that opened the limit. Also check for loose wiring connections.
Remove the top right electrical cover and inspect the connector. Ensure a jumper is installed across the MAN LIMIT terminals if not using a manual reset external limit. Ensure a jumper is installed across the AUTO LIMIT terminals if not using a automatic reset external limit.
HIGH TEMP LIMIT Reset using manual reset screen on display Verify all isolation valves are open and circulators are programmed into the control module properly. The internal boiler circulator can be configured to turn on or off with DHW and heating zones. Refer to the control module Setup section to configure these properly for the system.
Verify water pipe is installed correctly per instructions in this manual.
Verify proper circulator sizing for boiler size and system requirements.
See message displayed TEMPERATURE SENSOR and follow procedure for loose connections.
FLAME FAULT Reset using manual reset screen on display Burner may be operating too hot due to incorrect combustion. Inspect flame and conduct combustion test. Force boiler into hifire. Check flue gases with combustion analyzer and correct using the maintenance and startup procedure in this manual.
Verify FLAME SIGNAL value quickly goes to zero on the DIAGNOSTICS – INPUTS screen when the gas valve closes.
Check for flame at burner via flame current with burner off. Turn boiler off and watch flame through observation port. If flame continues after shutdown replace gas valve and venturi.
GAS VALVE FAULT Control will do automatic retry; lockout if retry unsuccessful; retry 1 hour after lockout — restart if condition cleared, but lockout permanently if condition still present. Requires manual reset if control is in lockout Check wire harness connections between gas valve and control module.
Check resistance between control and gas valve.
If lockout reoccurs replace control module.
BLOWER FAULT Reset using manual reset screen on display; control module will check again after 1 hour and will automatically restart if condition is corrected Check wire harness for loose connections and pin engagement at blower connections, chassis mount connection through control housing, and control module. Unplug connection at blower and at control module and check continuity between ends. Blower is connected to both low voltage and line voltage harness.
Check Diagnostics – Inputs screen with boiler in standby mode and blower not running. If BLOWER SPEED is not 0 RPM then replace blower.
If blower does not rotate during ignition sequence check for 120V power at blower connection. If 120Vac power at blower motor and it doesn’t start replace blower. Check power at control module. If 120Vac is not present at control module when boiler is powered replace control module. Refer to repair parts section.
IGNITION FAULT Automatically resets after 1 hour or can be reset by performing manual reset on boiler. Check condensate trap for blockage allowing condensate to accumulate inside heat exchanger. Check ignition cable connection.
Fouled, worn, bent, or faulty igniter. Fouled igniters can be cleaned for additional use with fine grit sand paper or steel wool. Worn or badly fouled igniters should be replaced with the proper repair part. Igniter rods should be parallel with a 3.5mm (0.138in) spark gap.
Dirty burner and/ or heat exchanger will cause high back pressure and poor ignition. Follow procedure in maintenance section of this manual to clean burner and heat exchanger using flue cleaning tool and rinse method. Visual inspection of flueways will often will not be able to diagnose condition.
Check combustion settings on high and low fire and adjust per setup instructions if necessary.
Check incoming gas pressure with boiler off and at high fire. Adjust within limits on rating label.
Verify correct boiler model is selected in control and high altitude is selected for installations 5500ft above sea level.
Check ignition cable resistance. Should measure 1000 Ohms (+/- 50 Ohms)
Check for flue pipe and intake pipe restrictions or blockage
Check burner fasteners and gaskets
Check venturi gaskets and proper propane orifice bushing
Check condensate trap for blockage allowing condensate to accumulate inside heat exchanger