A cold house when your Tempstar furnace refuses to heat is more than an inconvenience—it’s a race against dropping temperatures. Before you schedule an expensive service call, many common problems have simple fixes you can complete in minutes. This guide walks you through each troubleshooting step with clear instructions, so you can get your heat back fast—or know exactly when to bring in a professional.
Start With the Thermostat
The thermostat is the brain of your heating system. If it’s not sending the right signal, the furnace won’t fire up, no matter how well the rest of the unit works.
Confirm the Mode and Temperature
Switch the thermostat to Heat mode. It sounds basic, but after a summer of cooling, many homeowners accidentally leave it in Cool or Off. Then raise the set temperature at least 5°F above the current room reading. The furnace only activates when the room temperature drops below the set point—if you set it just 1° above, the system may not call for heat.
Replace Thermostat Batteries
Weak batteries are a leading cause of intermittent or no-heat issues. Most thermostats use AA or AAA alkaline cells. Replace them yearly or whenever the display appears dim, flickering, or blank. Even if the screen still shows numbers, low voltage can prevent the signal from reaching the furnace. Use fresh, name-brand batteries—cheap ones leak and corrode contacts over time.
Check for Smart Thermostat Issues
If you use a Wi‑Fi thermostat, verify it’s connected to your home network. A dropped connection can freeze the schedule or lock the device in an unresponsive state. Restarting the thermostat (pull it off the wall plate for 10 seconds) often re-establishes communication with the furnace.
Verify the Power Supply
Your Tempstar furnace needs electricity to run the blower, igniter, and controls. A tripped breaker or an accidentally turned‑off switch is one of the quickest fixes you’ll find.
Reset the Circuit Breaker
Go to your home’s main electrical panel and find the breaker labeled Furnace or HVAC. A tripped breaker sits in the middle position (sometimes slightly shifted). Flip it fully to OFF, then firmly to ON. If it trips again immediately, do not keep resetting—that signals a short circuit or overload that needs an electrician.
Check the Furnace Power Switch
Many furnaces have a standard light‑switch mounted on the side or nearby on the wall. It’s easy to bump this switch off during cleaning or when moving boxes. Confirm the switch is in the ON position. If your unit has a disconnect box (a metal pull‑out handle), ensure it is fully seated.
Oil Furnace Reset Button (If Applicable)
For oil‑burning Tempstar models, locate the red or black reset button on the burner housing. Press it once and hold for 5 seconds, then release. Wait at least five minutes before trying to restart the furnace. Never press the button more than twice—pumping excess oil can flood the combustion chamber and create a dangerous situation.
Restore Proper Airflow
When airflow is restricted, the furnace overheats and triggers a safety shutdown. Two routine maintenance tasks prevent this:
Replace the Air Filter
Check your filter every 30 days during peak heating season. A filter that looks gray, dusty, or clogged should be swapped immediately. Use the manufacturer‑recommended size (typically 1‑inch thick for residential units). Installing a filter that’s too thick or too dense can actually starve the furnace of air—stick with a MERV 8 rating for a good balance of filtration and airflow.
Tip: Mark the date on the new filter’s cardboard frame so you know when to check again.
Unblock All Supply and Return Vents
Walk through every room and verify that registers are open and unobstructed. Furniture, rugs, curtains, and toys can block warm air from entering the space and reduce return airflow back to the furnace. Closed or blocked vents force the system to run longer and may cause the limit switch to trip. Vacuum vent covers monthly to remove dust buildup.
Inspect the Ignition System
Gas furnaces rely on either a standing pilot light or an electronic igniter. If the furnace hums but no flame appears, the ignition system is the likely culprit.
Standing Pilot Light
Older Tempstar models have a small blue flame that stays lit continuously. If the pilot is out, follow the relighting instructions on the furnace label (usually printed inside the access panel). A common cause of a blown‑out pilot is a draft or a dirty thermocouple. If the flame goes out repeatedly, the thermocouple may need cleaning or replacement.
Electronic Igniter (Hot Surface or Spark)
Most modern Tempstar heaters use a hot‑surface igniter (a glowing rod) or a spark igniter. If you hear the gas valve click but see no flame, the igniter may be cracked or failed. Look through the sight glass (if available) or remove the burner cover—a healthy igniter glows orange‑red within 3–5 seconds. A dull or non‑glowing igniter needs professional replacement.
Clean the Flame Sensor
A dirty flame sensor is one of the most common “no heat” causes. The sensor detects the flame and tells the gas valve to stay open. If it’s coated with carbon, the furnace will ignite briefly then shut off after a few seconds. Gently clean the sensor with a fine emery cloth or dollar bill. (You can find step‑by‑step instructions in our guide on keeping a gas oven running, which uses the same type of flame sensor).
Diagnose Blower and Capacitor Issues
The blower motor pushes heated air into your ducts. If the motor runs slowly or not at all, the furnace will overheat and lock out.
Listen for the Blower
After the burner lights, you should hear the blower motor kick in within 30–60 seconds. If the burner runs but no air moves, the motor or its start capacitor may have failed. A failing capacitor often produces a faint humming sound without the motor turning.
Capacitor Testing (Visual Only)
Look at the cylindrical capacitor mounted near the blower. A bulging top, leaking fluid, or rust indicates it needs replacement. Capacitors hold electrical charge even when unplugged—do not touch the terminals. Leave capacitor testing and replacement to a licensed HVAC technician.
Understand Error Codes (New Section)
Many Tempstar furnaces are equipped with a control board that flashes error codes through a small LED window. These codes pinpoint the problem faster than guesswork.
| LED Flash Pattern | Common Meaning | What to Do |
|---|---|---|
| 1 flash (continuous) | Ignition failure | Check igniter, gas supply, flame sensor |
| 2 flashes | Pressure switch stuck open or closed | Inspect vent pipe for blockage |
| 3 flashes | Limit switch open | Check filter and vents for airflow restriction |
| 4 flashes | Rollout switch tripped | Call a technician immediately—possible heat exchanger issue |
Note: Count the flashes between pauses. The exact code may vary by model year. Consult your owner’s manual or the label inside the furnace door for the specific code chart.
When to Call a Technician
Some problems require professional tools and safety training. Do not attempt repairs if you encounter any of these:
- Gas smell – Turn off the furnace immediately, open windows, and leave the building. Call your gas company or a qualified HVAC technician.
- Carbon monoxide alarm – Evacuate and call 911. A cracked heat exchanger can leak this odorless, deadly gas.
- Recurring breaker trips – Repeated electrical faults indicate a short or failing component that only a pro should diagnose.
- Blower motor not spinning – Motor replacement involves high voltage and spinning parts—leave it to an expert.
- Error code you can’t resolve – If the furnace locks out three times, the control board may be damaged.
A well‑maintained Tempstar furnace can last 15–20 years. Annual professional inspections catch small issues before they become no‑heat emergencies. For example, a clogged drain line can trigger a safety shutdown—this is something a tech can clear in minutes.
Frequently Asked Questions
Why does my Tempstar heater run but no warm air comes out?
The blower may be running but the burner isn’t lighting. Check for ignition failure (pilot or igniter), a dirty flame sensor, or a tripped rollout switch. Also verify that the gas valve is open.
How often should I replace the air filter?
Every 1–3 months during heating season. Use a MERV 8 filter for most Tempstar units. A dirty filter is the #1 cause of short cycling and overheating shutdowns.
What does it mean if my furnace clicks but won’t start?
Clicking usually indicates the igniter or gas valve is trying to operate. If you hear clicking but no flame, the igniter may be failed or the flame sensor is dirty. If you smell gas, turn off the system and call a technician.
Can I bypass the pressure switch to test it?
No. The pressure switch is a critical safety device that confirms proper venting. Bypassing it can lead to carbon monoxide poisoning or fire. Always replace a faulty switch with the exact OEM part.
My Tempstar heater is 10 years old—should I replace it?
If repairs are becoming frequent and parts are hard to find, replacement may be more cost‑effective. Modern condensing furnaces achieve up to 97% efficiency, compared to 80% for older models. The U.S. Department of Energy offers furnace efficiency guidelines to help you compare.
Conclusion
A Tempstar heater that won’t work often comes down to one of four things: thermostat settings, power supply, airflow, or ignition. By checking these yourself, you can resolve the problem in under 30 minutes and avoid an unnecessary service fee. When basic fixes don’t work, trust the complexity to a licensed HVAC professional—especially if gas, carbon monoxide, or electrical faults are involved.
Take a moment now to replace your air filter and test your thermostat batteries. A small bit of preventive care keeps your family warm and your furnace running reliably all winter. If you’re dealing with a different appliance issue, our troubleshooting articles cover common problems like a kitchen freezer not cooling or a water dispenser that stopped working—helpful resources when other home systems act up. Stay warm and stay safe.