Start here
Quick, low-risk steps
- If you smell gas or hear a CO alarm, evacuate and call 911 or the gas utility.
- Check your thermostat is set to heat and the temperature is above room temperature.
- Look at your furnace through the access panel—note any error codes or unusual signs without opening it.
- Record the furnace make, model, and any displayed error code.
- Use our symptom checker or guides to understand possible causes and prepare for a pro visit.
Homeowner paths
Choose the guide that matches the decision
What to Do When Your Furnace Won't Turn On
Practical, safe observations when your furnace won't start. Learn what to check before calling a pro, and when to leave the house immediately.
Open guide →Decision guideFurnace Blowing Cold Air: What to Check Safely
Furnace blowing cold air can be a simple thermostat setting or a serious safety issue. Learn safe checks, when to call a pro, and what to avoid.
Open guide →Decision guideFurnace Short Cycling: Safe Observations and Next Steps
Furnace turns on and off too often? Learn safe checks, what to record, and questions to ask a pro. No DIY repair—just practical steps for Minneapolis–St. Paul homeowners.
Open guide →Decision guideFurnace Making Noise: Safety Steps and Evidence to Share
Furnace noises can signal danger. Learn which sounds mean shut it down, what evidence to collect, and how to describe the noise to a technician.
Open guide →Decision guideFurnace Smells: Dust, Burning, and Gas Odor Uncertainty
Unusual furnace smells can signal dust burn-off, electrical trouble, or a gas leak. Learn safe first steps, when to leave the house, and what to ask a pro.
Open guide →Decision guideWhat Affects Furnace Repair Costs
Understand what influences furnace repair costs, from diagnostic fees to parts and labor. Learn what to ask before you approve work in Minneapolis–St. Paul.
Open guide →Start with Safety
Your family's safety comes first. Carbon monoxide is odorless and can be deadly. If your CO alarm sounds or you smell gas, act immediately—don't wait to see if symptoms appear.
Even if there's no immediate danger, a malfunctioning furnace can create risks. Always have a working CO detector on every level of your home and test it monthly.
- Leave the house and call 911 if you suspect a gas leak or CO buildup.
- Do not turn on lights, appliances, or phones inside if you smell gas.
- Schedule annual professional furnace inspections to catch safety issues early.
- Know the signs of CO poisoning: headache, dizziness, nausea, confusion.
Common Furnace Symptoms
Furnaces can act up in many ways. Recognizing the symptom helps you communicate clearly with a technician and avoid unnecessary repairs.
Our guides cover frequent issues like no heat, cold air, short cycling, strange noises, and odd smells. Each guide explains what might be happening and what to ask a pro.
- Furnace not turning on at all.
- Furnace blowing cold air instead of warm.
- Furnace turning on and off too frequently (short cycling).
- Unusual sounds like banging, squealing, or rattling.
- Smells like burning dust, gas, or electrical odors.
Tools to Help You Decide
Before you call for service, use our private, on-page tools to organize your thoughts. They don't replace a technician, but they help you ask better questions.
The Symptom Checker walks you through a series of simple questions to narrow down possible issues. The Heating Cost Estimator helps you understand how different factors affect your bill.
- Furnace Symptom Checker: answer a few questions to get possible explanations.
- Heating Run Cost Estimator: see how thermostat settings and weather impact costs.
- Both tools are free, private, and require no personal information.
- Results are informational only—always confirm with a licensed HVAC pro.
Repair or Replace?
When a furnace breaks down, you may wonder if it's worth fixing. Age, repair cost, and efficiency all play a role.
Our repair vs. replace guide helps you weigh the factors without pushing you toward a sale. We explain what questions to ask about parts, labor, and long-term savings.
- Consider the furnace's age and overall condition.
- Ask for a detailed repair estimate with part and labor breakdown.
- Get a second opinion if a replacement is recommended.
- Check if your existing warranty covers any of the work.
Take this with you
Evidence and scope checklist
- Is there any gas odor or CO alarm? If yes, evacuate immediately.
- What is the exact symptom (no heat, cold air, noise, etc.)?
- What is the furnace make and model number?
- Is there an error code displayed on the furnace board?
- Have you checked the thermostat settings and batteries?
- Is the air filter clean? (Check without opening sealed panels.)
- Do you have a recent utility bill to compare usage?
- Have you had annual maintenance in the last 12 months?
Common questions
What homeowners ask next
What should I do first if my furnace stops working?
First, ensure there's no gas smell or carbon monoxide alarm. If safe, check your thermostat settings and circuit breaker. Then note any error codes or unusual signs before calling a professional.
How can I tell if I need a repair or a new furnace?
Consider the furnace's age, repair cost, and efficiency. A pro can test the heat exchanger and other components. Our repair-or-replace guide lists questions to ask before deciding.
Are your tools a substitute for a professional diagnosis?
No. Our symptom checker and cost estimator are educational tools to help you prepare for a service call. Only a licensed HVAC technician can safely diagnose and repair your furnace.
Evidence
Sources used for this guide
Research checked July 31, 2026
- Home heating and carbon monoxide safetyU.S. Consumer Product Safety Commission
CO and heating safety; emergencies take priority over troubleshooting.
- Heating and cooling maintenance checklistENERGY STAR
Maintenance context and professional service boundaries.
Optional next step
Need an on-site professional?
Use the guide and worksheet first so you can describe the situation and compare the full scope. A referral is optional; you can also contact a licensed local provider directly.
We have not enabled a provider route for this site. Use the checklist to contact and verify local providers yourself; urgent hazards should go to the appropriate emergency or public service.