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.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.
Same failure, different stakes: 344 next to 205
The furnace control carries several output relays, and this site documents two Lennox codes for the same physical failure — welded contacts — on two different ones. Alert 344 is the Y1 relay: stuck closed, it runs the outdoor cooling unit when nothing asked. Alert 205 is the gas valve relay stuck closed, and the difference in what those two relays switch explains the difference in urgency: a stuck Y1 wastes electricity and confuses the cooling system; a stuck gas valve relay feeds gas without a command, which is why 205 carries a shut-things-down urgency this alert does not. In both cases Lennox's persistent-fault remedy is the same, because on the IFC the relays are soldered components, not sockets — the board is the serviceable unit.
What the fix costs
Costed honestly, this is a two-step ladder. Step one is a diagnostic visit at $75–150 in which the technician rules out a shorted Y1 wire — a shorted low-voltage run holds the circuit closed and produces exactly this alert for the price of a wiring repair. Step two, if the relay itself has welded, is the board: Lennox's stated remedy is replacing the IFC, and a control board runs $400–900 installed, with communicating-model OEM boards at the upper end. There is also a running cost while you wait — an outdoor unit cycling uncommanded is billed by your utility — so an intermittent 344 in the fault history is not a someday item once cooling season arrives.
DIY or call a pro
Nothing on this one is homeowner-serviceable — the relay lives on the furnace's main control board — but homeowner observation is unusually valuable because the alert self-clears five minutes after Y1 reads off. Before the visit: note whether the outdoor unit has been running or humming when the thermostat shows no cooling call, and when; check the thermostat's alert history rather than the live screen, since a sticking-but-not-stuck relay will have left a trail of appearing-and-clearing 344s there. Hand the technician that history. What not to do: pull the furnace door and probe the board, or repeatedly cycle power to make the alert go away — an intermittently welding relay is failing in one direction only, and the history you erase is the diagnosis.
What this looks like
From the outside, this usually shows up as there is no heat but nothing looks obviously wrong — that walkthrough covers what to check in order, and when it stops being a homeowner job.