If your thermostat is stuck, the first thing you should do is make sure your system isn't locked. Bumping into your thermostat or accidentally pressing the wrong button can result in it becoming locked, but unlocking it is a quick process.
The short answer is your furnace won't turn off due to some kind of error or malfunction within your furnace, thermostat, or HVAC system. It could be the wrong thermostat setting is being used, a clogged air filter or your thermostat itself is no longer working properly.
Turn your thermostat to the 'off' position... Then venture off to your home's breaker box. Find the breaker to your HVAC system, flipping it 'off'. Make sure the breaker is flipped all the way 'off,' then wait for 30-seconds. Turn the breaker back 'on.
It could (likely) be one of two things. Either the thermostat is sticking and not disengaging or you have a short in the wiring.
If your thermostat is battery-powered, low or dead batteries could cause malfunctions. Replace the batteries and see if that resolves the issue. Incorrect wiring or loose connections in the thermostat can lead to issues like incorrect temperature readings or an inability to adjust settings.
Redo the Thermostat Wiring
Other times, corrosion and lint can build up on the wiring and prevent the current from passing through. If either of these is the case, call an HVAC technician to inspect and redo your thermostat's wiring. They have the knowledge to get the issue fixed!
This is an easy problem to solve yourself by simply removing the plastic outer casing and, with a very soft brush, delicately brushing off its coil and contact surfaces. It is most effective to clean the thermostat first at its lowest setting, then again at its highest setting.
Check the Thermostat
Your thermostat controls your furnace and basically tells the unit when to turn on and off. It's often to blame when your furnace won't stop running. Sometimes having the heat turn off is as easy as adjusting an incorrect thermostat setting. Make Sure Your Thermostat is Set to “Auto”.
Heater Doesn't Work
If your thermostat is stuck open, you won't get any hot air in the cabin when you turn the heater on. That's because the heater gets heat from the engine through the cooling system. Usually, the heated coolant will pass through the heater core and blow that heat into the cabin.
A dirty air filter can get clogged and reduce air flow through your home's heating system. This means the air your furnace is heating isn't reaching your living spaces and causing your furnace to cycle on more often and work longer while it's on.
Due to corrosion or aging, your car's thermostat can get stuck in a closed position. If this happens, the thermostat will not let the coolant reach the radiator, and, as mentioned above, the engine will overheat, causing severe damage. One of the lesser-known issues is the polar opposite of overheating.
Turn your thermostat “off”, then flip the related circuit breaker “off”. Wait 30 seconds, then turn the breaker back “on,” then the thermostat. Set the thermostat to hot or cold, whichever you prefer, and your desired temperature. This should effectively reset it.
Most homeowners spend between $112 and $311 to repair a thermostat. Exact costs range from about $50 to $500, with a national average of $212. The price may will depend on factors like the model you own and whether it has a warranty.
If your heater keeps running and doesn't want to shut down, it could be a sign of a problem. An unresponsive heater is a common issue. It could result from a bad blower motor switch, a dirty filter, or an inoperable thermostat.
A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.
If your ducts are dirty, they can cause your unit to run for extended amounts of time. When ducts are clogged, they do not allow for proper airflow. This will keep your HVAC unit running to try to heat the entire home and to satisfy the setting on your thermostat.
Often, no heat in the home is a result of thermostat issues, whether they be true malfunctions or errors in settings. Whenever you notice no heat, check your thermostat first for troubleshooting. Make sure your thermostat is on – the display should be on as normal. If it's not, there could be a power issue.
Replacing a Thermostat. You'll pay between $15 and $300 for the unit in addition to labor ($65 to $100 per hour) to replace an old thermostat with a new one. However, installing a brand-new thermostat is more involved and, therefore, more expensive.
One of the most common issues is the thermostat. The wiring, switches, or heating sensors can fail on your unit. If this is the case, then you'll need to replace the thermostat with a newer model. A damaged primary controller can also cause the furnace to stay turned on.
If the boiler continues to run after the timer has been turned off, it means your boiler system needs to be examined further. A thermostat, programmer, timer, motorised valve, pump, and heating element are all common parts of the heating system and one of these components could be the cause of the issue.
If your heater won't turn off, the first thing you do is check the thermostat. The thermostat controls how the heating system runs. It detects the indoor temperature and signals the furnace to start or stop. So, if the thermostat malfunctions, it can signal the unit to run continuously.
To reset mechanical thermostats, simply turn off the thermostat and flip the circuit breaker. This can be done by going to the breaker panel and turning off the appropriate breaker switch for 30 seconds. After turning the breaker back on, turn the thermostat back on and the thermostat should be reset.
While there is a small chance that there is an issue with the running temperature of your engine, by far the most common issue with trouble code P0128 is a faulty thermostat. The exact location of the thermostat and issues related to a damaged thermostat may vary depending on your vehicle.