Lennox furnace Alert code 344: Y1 relay stuck on the furnace control

Alert 344 means the Y1 relay on the integrated furnace control is stuck. Y1 is the first stage cooling call, so a stuck relay can leave the outdoor unit running when nothing has asked it to.

Applies to: Lennox communicating gas furnaces on an S30, S40 or comparable communicating thermostat, as documented in the Lennox Residential Communicating Systems Alert Code Guide.

What it means

Y1 is the thermostat's first stage cooling output, and on a communicating system the furnace control passes it through to the outdoor unit. A stuck relay means that contact is closed when the control has not commanded it. Lennox is specific about where the part is — the relay is on the IFC, the integrated furnace control — and about the remedy if the fault persists, which is to replace the IFC. The alert clears automatically five minutes after the Y1 input is sensed off, so a relay that is intermittently sticking will produce a fault that appears and disappears rather than one that stays.

Most common causes

A Y1 relay on the integrated furnace control with welded or stuck contacts.
A control board fault driving the relay incorrectly.
A short in the Y1 wiring holding the circuit closed.
Age — relays are mechanical parts with a finite number of operations.

How to diagnose it

Note whether the outdoor unit runs when no cooling has been called for. That is the symptom this relay produces.
Check the fault history rather than the live display, since the alert clears five minutes after Y1 goes off.
Note whether the fault is intermittent, which is characteristic of a relay beginning to stick rather than one that has failed.
Nothing here is homeowner-serviceable.

How to fix it

Technician work on the furnace control board.
Lennox's own note is that if the issue continues the IFC should be replaced — the relay is not separately serviceable.
The Y1 wiring should be checked for a short before the board is condemned, since that produces the same reading at lower cost.

Notes

A stuck cooling relay on a furnace control is easy to misattribute to the outdoor unit, because that is where the visible symptom is. The fault is indoors.

All codes for this manufacturer

Lennox furnace alert codes — every code, with what differs between models.

Sources

Lennox Residential Communicating Systems Alert Code Guide, document 100017, March 2023 — Table 2, Alert Codes and Troubleshooting

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.