Lennox Repair in Denver

What Lennox owners in Colorado usually call about

Most Lennox calls we take in the Denver metro fall into a few patterns. In winter it is a furnace that lights and then shuts down, a furnace that runs the inducer but never ignites, or a high-efficiency furnace that locks out after a cold night because its condensate line or its intake and exhaust pipes iced up or drifted shut with snow. In summer it is an air conditioner that runs but does not cool, usually from a failed capacitor, a refrigerant leak, or a condenser coil clogged with cottonwood fluff or flattened by hail.

Altitude adds its own problems. Thin air means less combustion air and a weaker draft, so pressure switches on Lennox furnaces are more sensitive to a partly blocked vent, a sagging pipe or a cracked hose than they would be at sea level. If your Lennox furnace shows a pressure switch code in Colorado, the switch itself is often fine and the venting or condensate drain is the real issue. Our furnace repair visits start with venting, drains and gas pressure before any part is condemned.

Lennox furnace error codes: reading the display

Many current Lennox gas furnaces, including the SL280V series, use an integrated control with a small display that shows an 'E' code when something goes wrong. The table below lists examples from the SL280V installation instructions. Low pressure switch codes (E 223, E 224, E 227) are the ones we see most often at altitude, while E 240 and E 241 usually point to a dirty or poorly grounded flame sensor or low gas pressure.

Codes and their meanings vary by model and control board, so always check the label inside your furnace door or your model's manual. Note the code before you cycle power: turning the furnace off and on can clear it, and a written note of the exact code saves time on the service call. If you see the same code twice in a day, shut the furnace down and call rather than repeatedly resetting it.

Lennox warranty registration: the 60-day rule

Lennox requires eligible equipment to be registered within 60 calendar days of installation, or of closing for new construction. In Colorado, registration matters: for Merit and Elite series equipment it adds a 5-year parts-only extension (10 years of parts coverage total), or you can choose 3 years of labor plus 2 more years of parts instead. Dave Lennox Signature Collection equipment gets a 2-year parts extension (12 years total) or the labor option. California, Florida, Georgia (for installs from January 1, 2026) and Quebec are exceptions where coverage applies without registration; Colorado is not on that list.

Before any Lennox repair, find your model and serial number on the furnace or condenser label and check whether the unit was registered. Manufacturer warranties typically cover the part, not the labor to install it, unless you chose a labor option. We will tell you in writing which parts may be covered so you can file the claim correctly.

Altitude notes for Lennox furnaces

The SL280V installation instructions say the furnace may be installed up to 4,500 feet without modification. Above that, which includes Denver, Castle Pines and most of the metro, the manifold pressure, gas orifices and pressure switch may need to be changed using Lennox high-altitude kits listed in the manual. Kits differ by altitude band and gas valve, so the correct one depends on your exact model and elevation.

If your Lennox furnace has run poorly since the day it was installed, it is worth confirming the high-altitude conversion was actually done. We check this on every Lennox heating call along with a combustion and temperature-rise test.

Repair or replace an older Lennox?

Lennox's newer ducted systems use R-454B refrigerant, and Lennox's ductless options use R-32, according to Lennox's 2025 refrigerant page. Lennox also says existing R-410A systems can still be repaired and recharged for the foreseeable future, though R-410A is becoming less available and more expensive. That means a leaking older Lennox air conditioner is still repairable, but a large refrigerant leak on an aging system is a reasonable point to compare costs.

Our rule of thumb: repair when the failure is a single part on a system with years of life left; price out replacement when the heat exchanger, compressor or coil fails on equipment near the end of its life, or when repairs keep stacking up. We give upfront written pricing for both options. If you are weighing gas against electric heat, see our guide on heat pumps vs furnaces in Colorado and our notes on Colorado's gas furnace NOx rules before you choose a replacement furnace.

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How old is your Lennox? Type the serial number into our HVAC age decoder to see the build date.

Lennox Error Codes

Codes differ by model and control board. Check the chart on your unit's door panel before acting on any code.