Lochinvar Boiler Error Codes Explained

When a unit goes down, every minute counts when you’re diagnosing a system. Get through error codes easily when technicians have the right troubleshooting guide to help. Below we have Lochinvar boiler error codes explained for certified technicians who need fast, reliable answers in the field. From identifying fault codes to understanding what they signal within the system, we’ll help you pinpoint issues quickly so you can move from troubleshooting to repairing in no time. 

Troubleshooting Lochinvar Boiler Error Codes

Gas Pressure SW

This error code means the gas pressure switch contacts on the Low Voltage Connection board are open. Here are some solutions to resolve the problem:

• Check for loose/misplaced jumper on LVCB
• Check for device wired across gas  pressure switch terminals on Low Voltage Connection

Flow Switch/LWCO

The flow switch/LWCo error code means the optional flow switch or optional low water cutoff isn’t making. If those aren’t the problem then it is most likely a blown fuse. To resolve the issue try any of the following:

• Check boiler pump operation on call for heat
• Check boiler piping for obstruction or closed valves
• Verify system full of water and all air purged from system
• Check for loose/misplaced jumpers if flow switch or LWCO not installed on Low Voltage Connection B
• Replace fuse F3 on control board

Block Drain SW

This error code means the blocked drain jumper has been removed from the wire harness. Try any of these solutions to fix the problem:

• Check wire harness and replace jumper if necessary
• Check for loose wiring connection at wire harness plugs

Air Pressure SW

This error code comes up when the air pressure switch contacts are open. Take action with any of the following:

• Check wiring connections to switch
• Air intake lengths exceed maximum allowed lengths
• Check for obstructions/blockage in air intake pipes or terminations
• Check for blockage/ obstruction in reference hoses connected to air pressure switch
• Inspect burner for build-up
• Inspect heat exchanger for build-up
• Replace faulty air pressure switch

Flame Fail Ign

When the unit has failed to prove main burner ignition after four (4) attempts, this error message will be on the display. Here are some steps you can try to fix it:

• Check wiring harness connection at gas valve and main control board
• Inspect spark electrode and associated wiring for damage and connection. Replace as needed
• Check unit has proper electrical grounding
• Check incoming supply gas pressure is accurate
• Verify plastic hose from gas valve to air inlet is connected
• Ensure vent/air intake pipes correctly installed and there’s no obstruction
• Check gas valve voltage at 2-pin connection on side of main control board during ignition attempt. If no voltage present, replace main control board
• Check wiring between main control board and gas valve, replacing wiring as needed
• Check that valves have gas flowing and for pressure changes
• Inspect flame sensor and associated wiring, cleaning as needed
• Inspect burner for build-up and replace as needed
• Replace the main control board

Flame Fail Running

When the unit is running and loses the flame signal five straight times, the Flame Fail Running error will display. Try any of the following actions to help:

• Check wiring harness connection at gas valve and main control board
• Inspect spark electrode and associated wiring for damage and connection. Replace as needed
• Check unit has proper electrical grounding
• Check incoming supply gas pressure is accurate
• Verify plastic hose from gas valve to air inlet is connected and undamaged
• Ensure vent/air intake pipes correctly installed and there’s no obstruction
• Check gas valve voltage at 2-pin connection on side of main control board during ignition attempt. If no voltage present, replace main control board
• Check wiring between main control board and gas valve, replacing wiring as needed
• Check that valves have gas flowing and for pressure changes
• Inspect and clean heat exchanger

Flame Sequence

This error code happens when the flame detector circuit is seeing a flame signal while no flame is present. Check any of the following to help resolve this code:

• Check supply voltage for proper polarity
• Check external wiring for voltage feedback
• Check flame rod and make sure it’s clean
• Check internal wiring for bad connections
• Replace main control board

Outlet ARHL or Outlet MRHL

You’ll see either of these error codes when the outlet water temperature has exceeded the setting of the automatic or manual reset high limit. Use the following to try and resolve the error:

• Adjust set point of auto reset limit to higher setting up to a maximum of 200°F or 210°F
• Verify system full of water and all air properly purged from system
• Check boiler is piped properly into heating system
• Check voltage to boiler pump motor on call for heat. If voltage not present, check wiring back to main control board
• If 120 Vac present on call for heat and boiler pump not operating, replace pump
• If system pump is variable speed pump, ensure system flow not less than boiler flow
• Check temperature setting of main control board
• Check resistance of water sensors
• Replace main control board as needed

Louver Proving Sw

The Louver Proving Sw code happens when an optional remote proving switch isn’t making. You can do either of the following:

• Check function of remote devices
• Check for loose or misplaced jumper if auxiliary proving switch not installed on Low Voltage Connection Board

Fan Speed

You’ll see a fan speed error code if the actual fan RPM is 30% lower or higher than what is being called for or a blown fuse. 

• Vent/air intake lengths exceed maximum allowed lengths
• Check for obstruction or blockage in vent/air intake pipes or at terminations
• Inspect wiring connections at fan and at main control board
• Replace fan
• Replace main control board
• Replace fuse F2 on control board

Low 24 vac

When the 120 Vac input to the main control board has dropped below 80 vac, the low error will be on the display. To resolve this error code, try any of the following:

• Check 120 Vac supply to transformer
• Check wiring connections at low voltage terminal strip
• Check wire size/length to remote devices
• Replace transformer

Fatal Error

When the control module has detected parameter settings that are out of range, a fatal error will be on the boiler display. The two ways to resolve this error is by restoring the parameter defaults from the software or by replacing the control module. 

Memory Error

This error happens when a lockout occurs at the same time as a power outage. To resolve the error, reset the control module.