Lennox SLP98UHV Error Code E 274: Soft Lockout - Limit Circuit
What Does Code E 274 Mean?
On the Lennox SLP98UHV, E 274 is a soft lockout triggered after the limit circuit opened on repeated recycles, or stayed open longer than 3 minutes. The furnace has stopped trying to heat and holds in a soft lockout before it will attempt to run again on its own.
E 274 is the escalation of E 250 (a single limit-switch trip). Where E 250 is one overheating event, E 274 means the furnace recycled and overheated several times in a row — a persistent condition the board refuses to keep fighting. It shares its root cause with the rest of this board's airflow family: E 252 (discharge air too hot), E 291 (measured airflow below the minimum firing rate), E 311 (heat rate cut back from low airflow), and E 312 (airflow cutback in cooling or fan mode). Because it is a soft lockout rather than a hard one, the SLP98UHV will retry automatically after the lockout interval, but it will simply lock out again if nothing has changed.
The most common homeowner-fixable cause is a dirty air filter that repeatedly starves airflow and lets the furnace overheat. Closed or blocked registers do the same. The important detail with E 274 is the order of operations: fix the airflow restriction first, and only then power-cycle the furnace to clear the soft lockout. Clearing the lockout without fixing airflow just sends the furnace straight back into the same overheating loop. Deeper causes — a failing blower or undersized ductwork — need a technician.
What You'll Notice
- The furnace is completely idle and will not start, sometimes for up to about an hour
- In the lead-up, the furnace ran in short bursts with the blower cycling repeatedly
- The 7-segment display shows E 274, and E 250 may appear in the code history
- The home has gone cold because the furnace is locked out
- The air filter is dirty or several vents are closed or blocked
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Persistent airflow restriction causing repeated overheating | Most common | ✓ DIY fix → |
How This Is Diagnosed
Because E 274 is a repeat-overheat lockout, the airflow path is worked first: filter, then registers, then visible ductwork. Only after airflow is confirmed restored is the lockout cleared with a power-cycle. If the furnace overheats and locks out again with good airflow, a technician looks at blower speed, gas input, and duct sizing.
How to Fix It: Restore Airflow, Then Clear the Soft Lockout
What You'll Need
- Replacement air filter (matching size) 🛒 Find at FiltersFast · 🛒 Find at Amazon
- Flashlight
Steps
- Turn off electrical power at the breaker and shut off the gas supply valve Switch the furnace breaker to OFF and turn the manual gas shutoff valve to the OFF position (handle perpendicular to the pipe), and let the furnace cool fully. If you smell gas, leave immediately and call your gas company.
- Replace the air filter Pull and inspect the filter. If it is dirty, install a new one of the correct size with the airflow arrow pointing toward the blower. If you recently moved to a high-MERV filter, switch back to the MERV rating Lennox recommends, since the extra resistance can cause repeated overheating.
- Open every supply register and return grille Walk the whole house and make sure all supply registers and return grilles are fully open and clear of furniture, rugs, and curtains, so airflow is no longer being choked.
- Inspect accessible ductwork Check any visible ducting for collapsed flex duct, disconnected sections, or crushed runs that would keep restricting airflow even with a clean filter.
- Restore power and gas to clear the lockout, then test Only after the airflow cause is fixed, turn the gas valve to ON (handle parallel to the pipe) and switch the breaker to ON. Cycling power clears the soft lockout. Set the thermostat to call for heat and watch several cycles, since E 274 is about repeated overheating.
When to Call a Professional
Contact a licensed HVAC technician if:
- E 274 or E 250 returns after replacing the filter and opening all vents
- The blower sounds labored or is not running at full speed
- The limit trips within minutes of each start before locking out
- E 252 (discharge air too hot) shows up alongside the lockout
- You suspect the ductwork is undersized for the furnace capacity
Frequently Asked Questions
How long does the soft lockout last?
The SLP98UHV holds the soft lockout for a set interval — often around an hour — and then retries on its own. Cycling power at the breaker clears it immediately, but you should only do that after fixing the airflow cause, or it will just lock out again.
What is the difference between E 250 and E 274?
E 250 is a single high-limit trip from overheating. E 274 is the soft lockout that follows when the limit trips repeatedly, meaning the overheating has happened several times and the underlying airflow problem is persistent.
I cleared the lockout but it came right back — what did I miss?
Almost always the airflow restriction was never actually fixed. Recheck the filter, confirm every register is open, and look for blocked returns or crushed ducting before clearing the lockout again.
✓ Verified against manufacturer service manual — March 2026