Why Is My Heating Still ON When Thermostat Is OFF?

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It can be a strange experience when you turn off the thermostat, but the heater refuses to go off. Nevertheless, it happens and can cause significant discomfort.

In most cases, the problem is usually the thermostat. A wrong thermostat setting could leave the heater running even after you switch the thermostat. Alternatively, it could a malfunctioned thermostat. However, it may also be something completely unrelated to the thermostat. Let’s find out.

Why You Should Be Concerned

First off, it’s important to discuss why heating remaining on even when the thermostat is off should be a concern.

Overheating in the home

The first main concern is that if heating continues even when you switch it off at the thermostat, you may have to overheat in the home. Usually, you want the home around 68˚F in winter.

However, if the heater continues running even after the desired temperature is achieved, you may soon have indoor temperatures at 80˚F or higher, which is uncomfortable and unhealthy.

Higher power bills

Your heating power bill depends on three main factors, i.e., the appliance’s power rating, power prices in your area, and how long you run the heater. If the first three factors are kept constant, the power bill will primarily depend on how long the heater runs. If the heater doesn’t turn off even after the thermostat is turned off, you could have a very high bill.

Accelerated wear

Heating appliances experience wear and tear just as other human-made machines and appliances. It’s exactly like your car. Every second spent on the road leads to wear further and tear.

It means that if the heater refuses to turn off, wear and tear is accelerated. Overheating in the motor and fan can cause some parts to malfunction within a few hours.

Risk of fire

Finally, you can never discount the risk of fire. According to the National Fire Protection Agency, local fire departments respond to about 48,500 fires involving heating appliances every year. A “rogue” heater that refuses to go off could easily have the same consequence.

4 Reasons Why your Heating Still ON When Thermostat Is OFF

Experts have identified four reasons why your heater may refuse to go off even when you turn off the thermostat;

1. Incorrect thermostat settings

In most cases, you’ll find that your heater isn’t going off because the thermostat is set incorrectly. Maybe you think you’ve switched it off, but it’s indeed on.

The confusion often arises when you can’t interpret the thermostat settings correctly. Many thermostats have either Heat, OFF, and Cool settings or Fan, Auto, and OFF settings.

However, others, especially those without a COOL setting, may only have an AUTO and FAN setting. Some may also not have a specific OFF setting. Instead, you may be required to turn the temperature knob to the lowest setting.

It can be confusing if you’re used to a different set of controls but have to use an entirely new set of controls. For instance, if you’re used to switching to the COOL setting but can’t find it on the new heater, you might try to select the FAN setting or another option that doesn’t necessarily turn off the heater.

Solution: See if you can find the OFF button. This usually turns off the heater right away. Alternatively, set it to the COOL mode or locate the speed settings and set the thermostat to the lowest heat setting. Then wait for 3-5 minutes. If it goes off, then it’s a thermostat setting problem. Otherwise, proceed to step two.

2. The thermostat has malfunctioned

For furnaces, begin by checking the two switches that may cause the blower fan to run continuously even if the furnace is not heating air. These are the thermostat switch and the limit switch.

Thermostat switches are found on the thermostat, while the limit switch is a manual push-pull switch located at the limit control in the air handler.

If both switches are functioning appropriately, it’s time to check the thermostat. Begin by checking that the two wires connecting it to the rest of the heating system are firmly attached. In most cases, it’s a red and white wire.

If both are fine, follow the wires from the thermostat to the control board in the heating system. Are the wires connected to the right terminals? Do they attach firmly to the terminals? These are some of the questions to ask.

Pro tip: If you’ve never handled electrical wiring before, you may want to hire an electrician for the final step.

3. It’s damaged thermostat wiring

This entire process is best handled by an electrician. You should only attempt it if you have confidence in your DIY skills.

Start by disconnecting the thermostat wires. This should be easy after going through step two. All you need to do is pull out the red and white wires that connect to the thermostat. Remember to do this only for the “rogue” air handler if dealing with a multi-zone heat pump.

Since the thermostat is essentially an ON-OFF switch that tells the heating system to run or go off in response to ambient temperatures, disconnecting the wires should turn it off. If it doesn’t go off, proceed to disconnect the wires at the heating equipment.

If the heating goes off, then the thermostat wiring is likely damaged/shorted. Shorting is the same as calling for the heater to heat. If the heater still won’t go off, it’s not a thermostat problem.

4. What else could be the problem?

It could be several things. We recommend that you turn the power off from this step onwards and call your HVAC providers to assist. Leaving the rogue heater on for a prolonged period creates an unnecessary fire risk while at the same time leeching on electricity or gas. So, turn it off as you wait for the HVAC technician.

Once the technician arrives, they’ll focus on a few specific areas. First, they’ll check to verify that the primary controller on the heating system is working correctly. A sticking primary control system on a heating system can cause the appliance to keep heating even after the thermostat says “enough.”

If it’s a hot water heating system, they may also check to see if unwanted gravity or convection is causing hot water circulation. This issue may result from baseboard and radiator defects. Most hot-water heaters have a special valve intended to prevent water from circulating on its own. However, this valve can malfunction too.

Know When to Call the Pros

A rogue heating system that refuses to go off even when you turn off the thermostat is a risk to yourself, your family, and even the home. If you don’t take appropriate action, you could soon be dealing with a fire.

Even if it doesn’t start a fire, the heater itself may get damages as the motor is overworked and overheated. It only takes a few hours for an overworked motor to burn out. This can necessitate costly replacement.

Therefore, it’s important to know what you can do to salvage the situation and when to call the pros. If you’ve tried everything and the heating still won’t go off, unplug the heater, turn off power at the mains panel, and call an HVAC technician.  

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