If your furnace isn’t firing, start with the thermostat, the breaker, the furnace switch, and the air filter before calling anyone. Those four checks resolve the majority of “my furnace won’t start” calls we get. If you’ve tried them and the system still won’t run, call us during business hours and we’ll get you on the schedule. If you smell gas or your carbon monoxide detector sounds, skip the checklist and call your gas utility and 911 immediately.
Start With the Quick Fixes
I’ve been answering calls like this for 30+ years in Salem, Keizer, and the surrounding Mid-Willamette Valley. A surprising number of “broken furnace” situations resolve with a five-minute checklist at the thermostat or electrical panel. Work through these before you call a technician.
Check the thermostat
- Confirm it’s set to Heat (not Cool or Off)
- Confirm the temperature setting is higher than the current room temperature
- If it’s battery-powered, replace the batteries
- Try switching the fan from Auto to On — if the blower runs in On mode, that confirms at least the blower circuit is working
Check the circuit breaker
Head to your electrical panel and look for a tripped breaker in the furnace circuit (usually 15 or 20 amps, sometimes labeled “Furnace”). If it’s tripped, flip it fully to Off and back to On.
If it trips again immediately, stop resetting it. That’s a sign of a real electrical problem, and repeatedly resetting it can damage the furnace.
Check the furnace power switch
Most furnaces have a standard-looking light switch mounted on or near the unit, often in a red box. It’s there so a service tech can kill power quickly. Anyone cleaning a utility closet or storage room can easily flip it off by accident.
Make sure it’s in the On position.
Check the air filter
A clogged filter is the most common cause of intermittent furnace problems I see — and it’ll sometimes shut a furnace down entirely as a safety. Pull the filter out and hold it up to a light. If you can’t see light through it, it’s overdue. Replace it with a fresh one and try the furnace again.
While you’re there, look at the return vent grille — if it’s caked with dust, vacuum it.
If Those Didn’t Fix It
There are a handful of other things worth glancing at before you call us.
Check the condensate drain (high-efficiency furnaces)
A 90%+ AFUE furnace produces condensate as it runs. That water exits through a small drain line. If the line is clogged, many modern furnaces have a float switch that shuts the unit down as a safety. The switch is there to keep water out of your burners.
If you see water around the base of the furnace or in the drain pan, that’s your clue. Clearing the drain is usually a simple job but often worth calling us for, because debris upstream of the switch is a sign of condensate pump or slope issues worth evaluating.
Check the flame sensor (older furnaces)
A flame sensor is a thin metal rod in the burner assembly that confirms the flame is lit. Over time it gets coated with carbon residue and loses sensitivity. The furnace will light, run for a few seconds, then shut off — and it’ll try again a few times before locking out.
This is a 10-minute cleaning job for a technician. It’s not really a DIY task unless you’re comfortable with gas equipment, and it’s often the cause of “cycles on and off” complaints.
Check the thermostat wiring connections
A loose wire behind the thermostat (common in homes where a thermostat was recently replaced or bumped during a wall paint job) can interrupt the call for heat. If you’re comfortable removing the thermostat faceplate and checking that the wires are snug in their terminals, it’s worth a look.
When to Skip the Checklist and Call Immediately
Some situations aren’t troubleshooting situations. They’re safety situations.
You smell gas
A strong sulfur or rotten-egg smell means a gas leak. Leave the house immediately with everyone inside, don’t flip any light switches on the way out, don’t use your phone inside, and once you’re safely outside call your gas utility and 911. NW Natural’s gas-leak response number is printed on your bill and on their website. Call us once the gas company has cleared the home, and we’ll diagnose and repair.
The pilot flame is yellow or orange
On older gas furnaces with a visible pilot light, the flame should burn blue with a small yellow tip. A flame that’s mostly yellow, orange, or flickering indicates incomplete combustion — which can produce carbon monoxide. Turn the furnace off at the switch and call.
Your carbon monoxide detector sounds
Get everyone out of the house. Call 911. Do not re-enter until responders clear the home. CO is odorless and fast-acting, and symptoms (headache, dizziness, nausea) often come on gradually enough that people don’t connect them to the source until it’s serious.
Every Salem home with a gas furnace, gas water heater, gas range, or attached garage needs functional CO detectors. Check yours now if you haven’t recently.
You hear unusual banging, booming, or loud mechanical noises
A loud bang at startup can indicate delayed ignition — a gas buildup inside the combustion chamber before the igniter fires. That’s not a wait-and-see situation. Shut the furnace off and call.
What to Do While You Wait for a Technician
If you’ve called and the furnace isn’t running, a few practical steps for keeping the house comfortable in the meantime:
- Close off rooms you don’t need to heat to concentrate warmth in shared spaces
- Run ceiling fans in reverse (clockwise looking up) on low speed to push warm air down
- Close curtains and blinds at night to reduce heat loss through windows
- Layer up, use blankets, and avoid opening exterior doors more than necessary
- Do NOT use your oven with the door open as a space heater — it’s a carbon monoxide risk in homes without adequate ventilation
Safe electric space heaters are fine for short-term use in a single room. Keep them at least three feet away from furniture, never leave them unattended, and plug them directly into a wall outlet (not an extension cord).
When to Plan a Replacement Instead
If your furnace is older than 15 years and it’s giving you repeated trouble, replacing it may be the smarter move than another repair. See our article on furnace replacement for the full decision framework.
Quick check: if the furnace is over 15 years old AND the repair would cost more than 50% of a new system, replacement usually makes better financial sense than repeated fixes.
How We Do It at CHS
We book appointments during business hours and show up when we say we will. Our technicians are salaried, not on commission — so the advice you get is the advice we’d give our own family. We tell you honestly whether your furnace needs a simple fix or if it’s time to start planning for a replacement.
Serving homes across Salem, Keizer, Dallas, Monmouth, Independence, Silverton, Stayton, Aumsville, Sublimity, Albany, Woodburn, Scio, and the surrounding Mid-Willamette Valley. Family-owned since 2001. Licensed and insured under CCB# 147550.
Related Reading
- HVAC Troubleshooting Basics
- When It’s Time to Replace Your Furnace
- Signs Your Furnace Is Ready to Be Replaced
Ready to Talk to Stan?
No pressure, no surprises — just honest advice from a team that’s been keeping Salem homes comfortable since 2001.
Call or text: (503) 581-6999
Email: chssatt@gmail.com
Service area: Salem, Keizer, Dallas, Monmouth, Independence, Silverton, Stayton, Aumsville, Sublimity, Albany, Woodburn, Scio, and surrounding Mid-Willamette Valley communities.
Licensed & insured: CCB# 147550
If you’ve worked through the checklist and the furnace still isn’t firing, call or text during business hours and we’ll get you on the schedule. A free estimate covers the diagnosis and walks you through the options.