Furnace Repair in Portland & Southern Maine

Air is moving but it's not warm, which points at the ignition or burner side: a failed igniter, a dirty flame sensor (a surprisingly common and cheap fix), or a gas valve issue. This is different from a blower or airflow problem and usually a faster repair than homeowners expect.

A furnace that fires briefly and shuts off repeatedly is often tripping its high-limit switch — a safety control that shuts the burner down if the heat exchanger gets too hot, usually because airflow is restricted. A dirty filter is the single most common cause; a failing blower motor or a closed-off duct run are the next most likely.

If the furnace doesn't respond to the thermostat at all — no blower, no ignition attempt — check the power switch (often a light-switch-style disconnect near the unit), the breaker, and the furnace's own fuse before assuming it's a major failure. Beyond that, it's a control board or transformer issue that needs a technician.

Trane

Trane's own troubleshooting page keeps it simple for the light on the control board: a slow, steady green blink just means the thermostat isn't calling for heat, and a fast green blink means the furnace is actively running. It's the red light homeowners write to us about, and Trane is upfront that the exact blink pattern behind a red fault is specific to that furnace's own control board — there's no single universal chart across their lineup.

Goodman

Goodman's GRVM97 and GDVM97 modulating furnaces use a dual seven-segment display that can show a stored numeric fault code on request — but the manufacturer's own spec sheet is clear that the number alone doesn't mean anything without that model's installation manual to translate it. What it's genuinely useful for is fault history: holding the board's switch for more than two seconds in standby recalls the last six logged faults, most recent first, which is exactly how we track down an intermittent problem that's already cleared by the time we arrive.

Carrier

The Carrier Infinity 98 (model 59MN7) owner's manual gives two instructions worth following before anyone touches the furnace: record the LED status code before cutting power or opening the access panel, since the code can be lost once power drops, and check that the burner flames read clear blue through the sight glass — a flame that isn't clear blue is a combustion problem the manual says to call a dealer for, not adjust yourself. We pull the stored fault history the same way before replacing any part.

Lennox

The Lennox SLP98UHV's Integrated Control lists roughly fifty diagnostic codes in its installation instructions. A handful come up far more than the rest on service calls:

Rheem

Rheem's RGFG installation instructions publish dozens of fault codes in Table 24, and note that the exact codes vary by control board revision. These three cover most of what we actually see in the field: