Nine times out of ten the thermostat fan switch is set to ON instead of AUTO — move it to AUTO and the blower stops at the end of the next heat cycle. If it is already on AUTO, the likely causes are a high-limit switch tripping because the furnace is overheating (usually a clogged filter) or a fan relay stuck closed, which is what a blower running with the thermostat fully off points to. Call (414) 429-5333 and Hub City will connect you with an independent local HVAC pro.
A blower that never shuts off is one of the most common calls Lubbock homeowners make in the first cold week of the season, and one of the few heating complaints with a free fix at the top of the list. Work through the causes below in order: the first takes ten seconds, the last needs a pro with the cabinet open.
Is the thermostat fan switch set to ON instead of AUTO?
Check this first: it is the most common cause and costs nothing to rule out. Nearly every thermostat has two separate controls, a system setting (HEAT / COOL / OFF) and a fan setting (ON / AUTO). On AUTO the blower runs only while the furnace is heating; on ON it runs around the clock whatever the temperature is doing.
Move the fan switch to AUTO. On a smart thermostat that control often sits in a menu labeled Fan and may offer a timed option such as “circulate” — choose AUTO instead if you want the fan to stop between cycles.
One thing to expect: after a heat call ends, a normal furnace runs the blower another 60 to 180 seconds to clear leftover heat out of the heat exchanger. That delay is designed in. If the blower stops within about three minutes of the burners going out, nothing is wrong.
Could a clogged filter be keeping the blower running?
Yes, and in West Texas it is the second thing to check. Every gas furnace has a high-limit switch that shuts the burners down if the cabinet gets too hot. When airflow is restricted the limit trips, the burners cut out, and the blower is deliberately left running to carry that heat away — which from the hallway reads as a fan that will not stop and a house that is not warming up.
- A filter loaded with caliche dust or cotton-harvest lint. A 90-day filter can choke in a month during harvest, so check it monthly through fall and winter.
- Closed or blocked vents. Furniture over a return, or registers shut to “save money,” raises pressure across the whole system.
- A collapsed or disconnected duct — see our guide to leaky air ducts and Lubbock energy bills.
- A dirty blower wheel or evaporator coil. Both load up with fine dust and both need a pro to clean properly.
Fit a clean filter of the same size and rating, open every register, and give it an hour. If the blower returns to normal cycling, that was the cause.
Blower running nonstop and the house still not warming up?One call and we'll connect you with a local Lubbock HVAC pro.
📞 (414) 429-5333What if the blower runs even with the thermostat off?
That narrows it to the furnace itself, and points at a stuck fan relay or failed control board. Set the system to OFF and the fan to AUTO. If the blower is still turning several minutes later, the thermostat is no longer asking for it — something inside the furnace is feeding the motor power it should have cut.
Usual suspects: a fan relay welded closed by years of switching, a failed component on the control board, or, on older equipment, a fan limit control whose contacts no longer open. A loose or shorted thermostat wire can mimic a permanent fan call too.
All of that is line-voltage work in a cabinet that also holds a gas valve and a live burner assembly, so it belongs to a licensed HVAC professional. Until then it is reasonable to switch the furnace off at its breaker or service switch. Do not leave it running for days — a blower turning against restricted airflow can overheat.
Is it bad to just leave the fan on?
It is not unsafe, but in a Lubbock winter it costs comfort as well as money. Between burner cycles the blower moves room-temperature air, which feels like a draft from the ceiling vents. It does have uses — evening out a sunny west room against a cold north bedroom, and running more air through the filter when dust is the real problem (see improving indoor air quality in Lubbock). For most homes, though, AUTO is the winter setting, as are the numbers in winter thermostat settings for Lubbock.
When is a blower that won't stop actually urgent?
- The burners are not lighting and the fan is circulating cold air — the overheat-and-lockout pattern, so the house will not stay warm.
- You smell burning, hot metal or anything sharply electrical. Shut the furnace off at the breaker and call — our post on furnace burning smells sorts the normal from the not.
- The motor is screeching or grinding. A failing bearing can seize, and a seized motor is a heat source.
- The furnace is also cycling oddly — see furnace short cycling in Lubbock, same overheating root cause.
Otherwise it is an annoyance and an electric bill rather than a hazard, and it can wait for a normal appointment.
Who should I call in Lubbock?
Hub City Heating & Air is a referral service, not a contractor, so we do not perform repairs or installations ourselves. Call (414) 429-5333 and we will connect you with an independent local HVAC pro who does. Start from our furnace and heating repair page, our AC repair page or our AC replacement page, or request a callback. Scheduling, pricing and guarantees are set by the independent contractor, and costs vary — call for a quote.
The cheapest version of this problem is the one you catch before the first freeze — our fall furnace prep guide for Lubbock is the short list worth working through now.
Frequently asked questions
Why won't my furnace blower turn off?
In most cases the thermostat fan switch is set to ON instead of AUTO, which tells the blower to run continuously whether or not the furnace is heating. If the switch is already on AUTO, the two next most likely causes are a limit switch that keeps tripping because the furnace is overheating, and a fan relay or control board that has failed closed and can no longer break the circuit. Check the fan switch first, then the air filter, then call a pro for anything inside the cabinet.
Is it bad to leave the furnace fan running all the time?
It is not dangerous, but it costs money and it can make the house less comfortable in winter. A blower running around the clock uses electricity continuously, and between burner cycles it circulates room-temperature air that feels like a draft coming out of the vents. Continuous fan does have legitimate uses, such as evening out temperatures between rooms or running air through a filter more often, but in a Lubbock winter most homes are better off on AUTO.
Can a dirty air filter make the blower run constantly?
Yes, indirectly, and it is a very common cause in West Texas. A filter loaded with caliche dust or cotton lint starves the return air, heat builds up inside the furnace cabinet, and the high-limit switch shuts the burners down for safety while leaving the blower running to clear that heat out. The blower then keeps running because the furnace never gets a clean cool-down, so the symptom you notice is a fan that will not stop.
How do I know if the fan relay or control board has failed?
The clearest sign is a blower that keeps running after the thermostat has been switched to OFF and the fan switch set to AUTO, with no heat call active. That points to a relay or board stuck in the closed position, feeding the blower power it should have cut. Diagnosing and replacing it means working on live line-voltage wiring inside the furnace, so it is a job for a licensed HVAC professional rather than a homeowner.
Should I turn the furnace off at the breaker if the blower won't stop?
If the blower will not stop and the thermostat is already off, switching the furnace off at its dedicated breaker or service switch is a reasonable short-term step, and it is what a pro will usually ask you to do while you wait. Do not keep running the system for days in that state, because a blower motor running continuously under a restricted airflow condition can overheat. Call for service rather than living with it.