🚨 Furnace Not Working? Mark’s DIY Troubleshooting Guide for the Goodman GR9S960803BN

Hey again — it’s Mark, your HVAC wingman. 
We’ve covered how to buy, install, and maintain your Goodman GR9S960803BN — and if you’ve been following along, chances are your system’s running like a dream. But let’s face it: even the best furnaces hit a hiccup now and then.

Now, I’m not saying you should crack open your gas valve and start poking around. But you’d be surprised how many issues you can handle on your own — no technician, no panic, no overtime charges.

So, in this guide, we’re going deep on DIY furnace troubleshooting. I’ll walk you through what to check, what the signs mean, and when it’s time to call in a licensed pro. Everything here is tailored to your Goodman GR9S960803BN, but honestly? These tips will save the day on most modern gas furnaces.

Let’s troubleshoot. 🔍

🛑 Before You Begin: Safety First, Always

Let me just say this loud and clear — never mess with the gas line, heat exchanger, or electrical panels inside your furnace unless you're trained and certified. The risks include carbon monoxide leaks, fires, voiding your warranty, and hurting yourself.

Stick to simple diagnostics and visible components. Anything beyond that? Call a pro.

Need help finding a qualified technician? HVAC.com lets you search certified, local pros by zip code.

Now let’s move on to the fun part.

🚫 Furnace Won’t Turn On? Start Here

Let’s say it’s freezing out, and your furnace is stone cold. Don’t panic — check the easy stuff first.

🔌 1. Power Supply

Even gas furnaces need electricity for the ignitor, blower, and control board.

• Check the furnace switch (usually mounted nearby, looks like a light switch) — it might’ve been flipped off accidentally.

• Inspect the breaker panel — if the HVAC circuit tripped, reset it once.

• Look for a fuse on the circuit board. If it’s blown, that could point to a larger issue.

Still no power? You’re likely looking at a control board issue or internal wiring. That’s pro territory.

🔥 2. Thermostat Troubles

The most common furnace issue I see? Thermostats on the wrong settings. Happens all the time.

Double-check:

• It’s set to HEAT, not COOL or OFF

• The temperature is set at least 3–5°F above room temp

• The batteries are fresh (if it’s not hardwired)

• The display shows a call for heat (usually indicated by “HEAT ON” or a flame icon)

Still unsure if it’s the stat? Try bypassing it with a jumper wire or temporary manual control. Family Handyman offers a great step-by-step for this.

💡 3. Furnace Lockout Mode

If your Goodman goes into lockout, it’s trying to protect itself after a failed ignition cycle.

Look for:

• A flashing LED diagnostic code on the control board (check the inside panel sticker for what it means)

• A solid red light = system failure or lockout

• A slow or fast blink = specific error (like flame sensor fault or pressure switch)

To reset:

1. Turn off the furnace at the switch

2. Wait 30 seconds

3. Turn it back on

If it resets and runs, great. If not? Let’s keep digging.

🌬️ Furnace Is Running… But No Warm Air?

If your system is “on” but cold air is blowing out — or nothing is coming out at all — here are a few common culprits.

🧽 1. Dirty Filter

We’ve said it a hundred times, but it bears repeating — clogged filters are your furnace’s worst enemy.

A clogged filter:

• Restricts airflow

• Can cause overheating and high-limit switch trips

• Makes your system short-cycle (turn on and off rapidly)

• Eventually shuts the whole thing down

If you can’t remember when you changed the filter, change it now. For the GR9S960803BN, a MERV 8–11 pleated filter does the trick.

For more on how filters affect performance, check out the EPA’s filter guide.

🌡️ 2. Overheating Shutoff

If your heat exchanger gets too hot — usually due to a dirty filter or blocked duct — the furnace shuts down to protect itself.

Signs:

• The burner lights, runs for a few minutes, then shuts off

• The blower keeps running, but there’s no heat

Turn off the system, change the filter, and let the furnace cool for 10–15 minutes. Turn it back on and monitor it. If it repeats? Time for a pro.

🔥 3. Ignitor or Flame Sensor Issues

Two common parts that fail over time:

• Hot Surface Ignitor (HSI): If it cracks or fails, no ignition occurs

• Flame Sensor: Detects if the burner flame is present — if it’s dirty or faulty, the gas shuts off for safety

You can clean a flame sensor with an emery cloth, but again — if you’re unsure, get a tech out. These are sensitive parts, and mishandling them can do more harm than good.

📉 Short Cycling? Furnace Turns Off Too Fast?

Short cycling = your furnace turns on and off too frequently. Bad for efficiency, and worse for your equipment.

Possible causes:

• Dirty filter (yes, again)

• Improperly sized system

• Blocked exhaust vents

• Bad thermostat placement (like near a window or heat source)

• Malfunctioning limit switch or flame rollout sensor

Start with the filter and thermostat location. If those check out, it’s worth getting a technician to do a full diagnostic.

This issue is especially common in homes where the furnace was replaced, but the ductwork wasn’t updated. The U.S. DOE says duct sizing and pressure are often overlooked — and it leads to early system failure.

🚿 Water Leaks Around the Furnace?

The Goodman GR9S960803BN is a condensing furnace, which means it creates water as part of the combustion process.

So, leaks are usually caused by:

• Clogged condensate drain

• Cracked condensate line or trap

• Improper drain line slope

• Disconnected fittings

Check the white PVC drain line and surrounding joints. Clear clogs with vinegar and warm water (don’t use bleach — it can damage tubing). HomeServe has a solid DIY guide on how to flush your condensate line safely.

Still dripping? You may need a new trap or line re-run. Not a huge job, but one best left to the pros.

📈 Blower Motor Won’t Stop Running?

When the blower won’t turn off — even when the heat stops — it’s likely:

• Thermostat fan is set to “ON” instead of “AUTO”

• High-limit switch tripped

• Blower relay stuck closed

Start by checking the thermostat setting. If that’s not the issue, turn off the furnace, wait 30 seconds, and power it back up.

If the blower starts immediately and won’t stop, the relay may be stuck, or you’ve got a bad control board. Time to bring in a pro.

👷 When to Call a Technician (and What Info to Provide)

Here’s my honest rule: if you’ve checked the basics (power, filter, thermostat) and still can’t pinpoint the issue — call a tech before it becomes a bigger problem.

Be ready with this info to save time (and money) on the service call:

• Model number (GR9S960803BN)

• Any LED diagnostic codes

• When the issue started

• What you’ve already tried

• Last time the unit was serviced

Your HVAC pro will appreciate it — and you’ll avoid paying for basic diagnostics they didn’t need to do.

🧠 Mark’s Troubleshooting Cheat Sheet