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Can Bad Thermostat Cause No Heat? (Read This First!)

We use many different appliances around our house to make our lives easier and to cater to our comfort. Many of these appliances use sensors to detect changes in the environment and operate accordingly. 

The thermostat is one such sensor that detects changes in the temperature and instructs appliances to change modes of operation.

Bad thermostat

A bad thermostat could cause no heat in both your car and your house. In cars, a bad thermostat could prevent the coolant from flowing through it and prevent the core from producing heat. In houses, bad thermostats can cause irregular turning on and off in your HVAC systems.

The thermostat is a device that is used to detect any changes in temperature and then send signals to devices or appliances to respond in such a way to maintain the desired temperature. 

When the temperature goes out of a boundary defined by the appliance, the thermostat detects this change and sends a signal to the appliance which then changes its mode of operation to bring the temperature of the target area within the desired range. 

The use of a thermostat in vehicles is commonly used to monitor the engine temperature to control the flow of fluid to the engine or the coolant to the radiator. And in houses, the thermostat plays a role in heating or cooling units to ensure the air is not too hot or too cold. 

Their ability to detect temperature changes also makes them useful in fire-detection alarm systems.

In a car: 

A faulty thermostat would cause the engine’s coolant to be the same temperature as the engine and prevent any generation of heat if the thermostat is stuck in an open position. 

However, if the thermostat is closed, the check engine light will turn on due to an overheated engine as the coolant cannot flow through. 

If the engine temperature keeps on running either too high or too low, not only will the engine’s performance decrease but also reduce gas mileage. If this continues over time – your engine will be severely damaged and will be expensive to repair.

In the house: 

A bad thermostat in your house would cause the heater or air conditioner to stop functioning properly and make them suddenly turn on or off in an irregular pattern. 

This is due to wrong signals being sent to the HVAC unit from the thermostat, which makes the HVAC respond to a false room temperature. Another telltale sign is that the temperature displayed on the thermostat display does not match the feels of your room. 

For a bad thermostat – if the room is hot the thermostat would display otherwise and vice versa.

3 reasons why a bad thermostat causes no heat

There are several reasons why a thermostat might cause no heat, whether it be in your car’s engine or your house. Below are some of the reasons why there could be no heat due to a bad thermostat: 

Open thermostat in the engine:

A coolant is a fluid that prevents the overheating of an engine by flowing through the radiator to cool the engine down. However, if the coolant is allowed to flow for an extended period of time, it would cool the engine enough to cause it to shut down.
A faulty thermostat would cause the engine’s coolant to be the same temperature as the engine and prevent any generation of heat if the thermostat is stuck in an open position

False temperature readings:

Most heaters rely on the temperature readings from the thermostat in order to regulate the heat and decide when to automatically turn on or off. 

A thermostat is responsible for sending signals to the heater according to the temperature readings but if the thermostat is bad, it could send the signal to the heater that the temperature is high – which would cause the heater to not generate heat.

Debris in the thermostat:

Another reason for no heat generation is often ignored – that is debris in the thermostat. Debris stuck in the thermostat could cause the thermostat to give high temperature readings and thus prevent generation of heat.

What are the symptoms of a bad thermostat?

There are several signs that can be observed to identify whether you have a bad thermostat or not. Below listed are some of the symptoms used to identify a bad thermostat:

Irregular sudden changes in temperature:

A bad thermostat will cause the entire air conditioning system to malfunction and change temperatures suddenly and irregularly. 

If you notice the thermostat temperature display, you will notice sudden changes in the temperature readings – which is an indicator of false temperature readings due to faulty thermostat.

Always high temperature reading:

The reason your engine is overheating is most likely due to a bad thermostat stuck in a closed position. As a result the coolant fails to flow through the valves to cool down the engine, and thus the engine’s temperature keeps on rising without anything to cool it down. 

This can be noticed by observing the temperature gauge in your vehicle as it displays an unusually high engine temperature.

Lower mileage:

If the thermostat is bad, the engine will be continuously at either an overheated or over-cooled state which damages the engine in the long term. 

If the engine is losing its efficiency, the fuel economy would be lower as well and thus require your vehicle to consume more fuel – thus resulting in a lower mileage. 

How do you know if your home thermostat needs to be replaced? 

There are some signs you would notice that are good indicators of the condition of your thermostat and whether you should replace it

If your HVAC suddenly turns on and off in an irregular pattern, that means something is wrong with the readings coming from the thermostat. A bad thermostat would fail to correctly communicate with your HVAC and thus cause it to malfunction. 

This can be further verified by observing the thermostat readings from the display in its dashboard. If your house is warm but the thermostat shows lower temperature or vice versa – that means your thermostat is failing to read the temperature of the area properly. 

Is it easy to fix a thermostat?

Whether it is easy to fix a thermostat by yourself is a complicated question to answer given that there are several types and brands of thermostats available in the market. 

Many of them have different designs – making them a bit of a challenge to fix yourself if you do not have prior knowledge about electronics.

However, it can be an easy procedure to fix or replace the thermostat yourself if you have a basic understanding of how electrical components work and know how to use basic tools that you would use. 

If you meet these requirements, you can easily replace the thermostat yourself while saving on costs.

How to fix a bad thermostat?

The steps below describe how you should replace a bad thermostat:

Remove the thermostat:

In order to remove the thermostat, locate its housing by tracing along the radiator hose up to the engine and locate the thermostat housing and remove the bolts using a wrench to uncover the thermostat. 

You can remove the radiator hose for the time being in order to make the task easier and move it out of the way. Once that’s done, loosen the clamp on the hose and then take off the assembly to expose the faulty thermostat. 

Placing the thermostat in the assembly:

It is important that you place the thermostat in the assembly in the correct orientation. The way to do it is to put the short end of the thermostat towards the hose and the deep end towards the engine.

Configuring the toggle switch:

Once you have figured out which way to put the thermostat, look closely into the thermostat to locate its toggle switch. You need to make sure the toggle switch is pointing straight up towards the top of the engine so that the air can get out faster. 

Installing the thermostat:

First put the thermostat into the housing on the engine, then place the top of the cover on it and screw the bolts back in place. Next, slide the radiator hose back on in place and use pliers to tighten the clamps. 

Finally, turn on the engine and turn on the heater at max and pour in some coolant as needed.

Final Thoughts

Both your vehicle and your home could be without heat due to a faulty thermostat. A faulty thermostat in a car could prevent coolant from flowing through it and the core from producing heat. Bad thermostats in homes might cause your HVAC systems to turn on and off irregularly.