A stuck thermostat is most commonly an issue with your car's engine cooling system or a household HVAC unit. The ideal fix depends on which type of thermostat you are dealing with:
Thermostat Stuck on One Temperature? 5 Fixes That Actually Work
A stuck thermostat can make it hard to warm up the cabin or keep the engine at the right temperature. That might not seem serious at first, but driving with a thermostat problem for too long can cause damage.
Generally, repairing a thermostat costs around $200 to $500. This is the price range you'll find for most vehicles, although some may be higher or lower depending on the circumstances. But if we're talking complete replacement, expect the price to increase by $50.
Then, get the thermostat and drop it in the pot of hot water (make sure it's deep enough to cover the whole thermostat) and carefully lower it into the water and observe it: at the temperature marked on the thermostat, it should quickly open the unit. If it does not fully open, it is stuck.
With safety precautions, the right tools, and a clear set of instructions, you may feel confident tackling the job yourself. But if you run into wiring issues, lack a C-wire, or just want a guarantee that it's done right, calling a professional is the best option.
Your heater uses engine heat. If the thermostat is stuck open and the engine runs cooler than normal, you might get weak cabin heat, especially at idle or in cold weather. It can feel like the heater never really gets going. A thermostat stuck closed can create the opposite situation.
Signs the Thermostat Is Stuck Open
The temperature gauge stays unusually low after several minutes of driving. Heater blows lukewarm or cold air, even when fully turned on. Reduced fuel efficiency, as the engine works harder to maintain performance. Increased emissions due to improper engine temperature.
Long-Term Effects of Ignoring a Bad Thermostat
Running an engine that's too hot can cause severe internal damage, while consistently running an engine too cold can result in a loss of power, increased fuel consumption, and even harmful emissions.
Corrosion, debris, or just plain age can cause them to stick. If your car is older or hasn't had the thermostat replaced in a long time, it might be time for a new one. Old or dirty coolant can also affect the thermostat.
A thermostat stuck in the closed position keeps coolant from flowing to the radiator. This can cause the engine to overheat, especially once it warms up and starts working harder.
Find an old sharp blade kitchen knife or a pocket knife with a stout blade. Insert the sharp edge of the blade under the edge of the thermostat housing and pound it into the gasket space by hammering on the back edge of the blade.
Average Lifespan of a Thermostat
With a straightforward design and basic scheduling features, they are reliable workhorses that can last 10 to 15 years with proper care. Routine programming updates and occasional recalibrations go a long way toward keeping them accurate and extending their usefulness.
If your thermostat uses batteries, try removing the cover and replacing the batteries. If it is a wired thermostat, there may be a problem with the thermostat wiring. Unless you're an HVAC technician or electrician, we don't recommend fiddling with the wires. Call an HVAC professional for assistance.
It is located between the engine and the radiator. Although a stuck closed thermostat can cause overheating, modern thermostats more often fail by opening too soon or sticking open, which generally causes the engine to run too cool.
The total varies with labor time (0.8–2.5 hours at $50–$220 per hour), the part type—basic ($15–$60) or integrated/electronic (a few hundred dollars)—and how difficult it is to access. Many vehicles allow for a do-it-yourself thermostat replacement if you can drain coolant, remove hoses, and torque bolts correctly.
Fortunately, you can still run your furnace without needing a thermostat should you rely on a fuel-powered unit for heat. One way to do so is by wire-nutting the white and red wires together; allowing the furnace to run without a thermostat.
There are 7 symptoms that can help your identify if you have a bad thermostat:
A thermostat that stays stuck open means your engine stays too cold. When your engine is cold, it burns more fuel than usual. This can lower your gas mileage and increase your costs at the pump.
A plumber isn't usually needed for thermostat replacement unless your thermostat directly controls a water-based heating system, such as underfloor heating or a boiler with complex plumbing connections. Even then, an electrician is typically the right professional to handle the wiring.
Average Cost of Thermostat Replacement
Thermostat Replacement starts at $99.
How can you tell if a thermostat is bad?