In Denver, your furnace isn’t just a winter appliance — it’s a year-round essential. With weather that can swing from sunny to snowy in the same week, homeowners rely on their heating systems more than most parts of the country. That’s why when a furnace acts up, it’s more than an inconvenience. It’s a disruption to your comfort, your safety, and your peace of mind.

At Done Plumbing, Heating, Cooling & Electric, we’ve spent decades serving Denver and the surrounding suburbs. We know the quirks of Colorado homes, from historic properties in Capitol Hill to new builds in Parker, and we’ve repaired, replaced, and maintained thousands of furnaces across every major brand. In this guide, we’ll share the most common furnace issues we see, explain when repair vs. replacement makes sense, and highlight how to stay ahead of costly breakdowns with regular care.

The Most Common Furnace Problems

Homeowners often notice furnace problems in subtle ways before they turn serious. Here are the issues our Denver technicians see most often:

Dirty or clogged filters. When filters are full of dust, hair, or construction debris, your system has to work harder, airflow drops, and your energy bills rise.
Ignition or pilot light failures. A furnace that struggles to start, or shuts off mid-cycle, may have ignition system problems.
Thermostat malfunctions. If certain rooms are too hot or too cold, or the system won’t turn on, your thermostat may be the culprit.
Blower motor problems. If warm air isn’t moving through your vents, a failing blower motor could be at fault.
Furnace blowing cold air. This common complaint often comes from clogged filters, ignition issues, or overheating that forces the system to shut down.
Strange noises. Rattles, bangs, or squeals signal loose parts, failing motors, or other issues you don’t want to ignore.

Knowing these warning signs can save you from waking up to a cold house on a snowy morning.

What’s the Most Expensive Furnace Repair?

Not all repairs are created equal. Some are quick and affordable, while others come with a hefty price tag. The heat exchanger is typically the most expensive furnace repair. It’s responsible for safely transferring heat from combustion gases into the air flowing through your home. If it cracks, not only is it costly to fix, but it can also pose serious safety risks.

Other big-ticket repairs include:

Blower motor replacements — essential for moving air through your ductwork.
Circuit boards — the control center for your furnace’s functions.
Draft inducers — vital for venting combustion gases.

When facing one of these repairs, it’s smart to weigh whether investing in a new system makes more financial sense.

The $5,000 Rule: Repair or Replace?

One of the most common questions we hear is, “Should I repair or replace my furnace?” That’s where the $5,000 rule comes in.

Here’s how it works:

Multiply the age of your furnace by the estimated cost of the repair.
If the total is less than $5,000, repair is often the better option.
If the total is more than $5,000, replacement usually makes more sense.

For example, say your furnace is 12 years old and the repair cost is $600. Multiply 12 x 600 = $7,200. Since that’s above $5,000, it suggests replacement might be more cost-effective long-term.

This rule isn’t absolute, but it’s a helpful way to put repair costs in perspective. Our technicians always walk Denver homeowners through both options so you can make the choice that fits your budget and your comfort.

Local Homes, Trusted Furnace Brands

Furnace problems don’t look the same in every home. Denver’s mix of old and new housing means our team sees it all:

Older homes often have outdated ductwork or space constraints, making modern furnace upgrades tricky.
Newer builds typically use high-efficiency systems from brands like Carrier, Trane, Lennox, and Goodman — all of which we service daily.
High altitude means certain ignition systems and airflow settings need expert adjustments to perform properly.

Because we’ve worked across every corner of the metro area, Done has the local experience to diagnose problems fast and fix them right the first time — no guesswork.

Warning Signs Your Furnace Needs Service Now

It’s not always clear if a problem is urgent. Here’s when it’s time to pick up the phone:

The furnace repeatedly cycles on and off.
Warm air isn’t reaching your rooms.
You hear loud or unusual noises.
The system blows cold air.
Energy bills spike unexpectedly.
Your carbon monoxide detector goes off.

If you’re wondering about carbon monoxide specifically, check out our post: Can a furnace leak carbon monoxide when turned off?

The Smart Way to Avoid Furnace Breakdowns

The best way to avoid breakdowns is simple: keep up with maintenance. Annual tune-ups clean out dirt and buildup, check safety systems, and ensure your furnace runs efficiently. Skipping maintenance often leads to surprise repairs and higher energy costs.

At Done, our Care Club membership makes maintenance easy. Members get annual furnace tune-ups, AC tune-ups, and a full plumbing check every year. That means we’ll flush your water heater, test shut-off valves, and make sure all your comfort systems are running smoothly. Plus, Care Club members enjoy priority service, 10% off repairs, and no dispatch fees. It’s the simplest way to protect your home year-round.

Your Local Furnace Experts, Ready 24/7

From rattling noises to costly heat exchanger repairs, Denver furnaces face challenges most homeowners can’t solve on their own. But with the right team on your side, you don’t have to worry about unpredictable weather or surprise breakdowns.

Done Plumbing, Heating, Cooling & Electric has been serving the Denver area since 1999. Our licensed, background-checked technicians are available 24/7, we work on all major brands, and every job is backed by our Home Comfort Guarantee.

If your furnace is giving you trouble, don’t wait for the weather to turn. Call Done today for reliable furnace repair service in Denver — and get the peace of mind that comes from having Colorado’s most trusted home service team on your side.