Why Is My Boiler Still Running When Thermostat Is Off

Warm water and a cozy room are what you need in the extreme cold season. For this purpose, homes, workplaces, and commercial properties use boilers. The basic function of a boiler is to produce hot water, which in turn, is used for heating and providing warm water to the entire building, through a well-crafted heating system.

Like any other home appliance, a boiler can also start malfunctioning at any time. The most common fault that every boiler user may often face is when the thermostat is off but the boiler keeps running. It seems that the thermostat might have developed a fault but that is not the only reason for a boiler running even if the thermostat is turned off. The boiler system comprises various parts that regulate its performance, such as a thermostat, timer, programmer, valves, and electric wiring and switches. Any of these parts may be the actual reason behind this type of fault in the boiler.

So, you need to conduct a complete inspection of the entire boiler system to find out the faulty component. But before that, you need to understand how a boiler works. This will help you find out the actual fault and how to fix it.

How a Boiler Works?

A boiler is used to heat the water. Whatever may be the size and wherever the boiler might be installed, the basic process of working on a boiler is almost the same. A boiler needs the energy to heat the water. Most boilers use gas for this purpose but some other types of boilers operate on coal, oil, and electricity.

Water is heated in an inner vessel of the boiler. The hot water is then circulated in the heating system, often in liquid form, whereas some types of boilers convert this hot water into steam before circulating it into the system. The heating system in a building consists of pipes, blowers, and radiators.

The heated water circulates through the pipes and radiators, installed in different locations, per the requirement. The air that comes in contact with this hot water also gets heated. This hot air is then blown into the rooms, through blowers. Similar is the process of heating the water for washrooms and kitchens.

Main Components of a Boiler

Though it also depends on the make and model of the boiler, generally it consists of the following main components:

• Burners
• Heat exchanger
• Controls
• Tubes
• Valves
• Thermostat
• Timer
• Programmer
• De-aerator
• Piping
• Electric Wiring
• Control Panel

Process of Heating the Water in a Boiler

The process of heating the water is very important for the working of a boiler. Based on this process, boilers can be classified into two different types:

• Fire Tube Boilers – In this type of boiler, the combustion takes place in the fire tubes, which are situated inside the main water compartment, also referred to as a pressure vessel. As a result of combustion, the tubes get heated. This heat is transferred to the water flowing around these tubes when water comes in contact with these tubes. This type of boiler is mainly used in homes.
• Water Tube Boilers – Here the water flows through the tubes and combustion takes place in the shell, surrounding these tubes. The heat produced in the shell is transferred to the water flowing through the tubes. This type of heating process is useful where very high pressure is required, around 3,000 PSI or even more. This type of boiler is more useful for industrial purposes.

Role of Thermostat

The hot water, produced by the boiler is transported to the heating system of the building. Passing through the entire heating system, the temperature of the water drops. This relatively colder water is then circulated back to the boiler for heating again. This flow of water to and from the boiler keeps on running continuously. During this process, the boiler keeps on heating the water to the pre-set temperature.

A thermostat regulates this process. When the temperature reaches the pre-set level, the thermostat shuts off, resultantly, the boiler stops heating the water. When the temperature of the water drops, the thermostat turns on and the boiler again starts heating the water. Hence the thermostat is the device that controls the water heating process in the boilers. The thermostat also maintains a constant temperature of water in the boiler.

Role of Timers and Programmers

Timers and programmers are also used to turn on and turn off the boilers at a pre-set time. A timer is used to start and turns off the boiler automatically at a fixed time, every day. The starting and turning off time can be changed as per the requirements. Similarly, a programmer enables a boiler to automatically start and turn off on pre-determined days and times, weekly or monthly.

However, the thermostat still keeps on working in both these cases. While the role of the timer or programmer is to start and turn off the boiler at a fixed time, the thermostat controls the temperature of the water to avoid overheating. So, the thermostat works in collaboration with the timer or the programmer.

What happens When the Thermostat Shuts Down But the Boiler Keeps Running?

Though quite a common problem that you may often face, it has some serious consequences, when the boiler keeps running even if the thermostat or timer is off. The purpose of installing a thermostat or timer is to control the heating process of the boiler.

The timer shuts down at a pre-set time so that the boiler should stop running. The thermostat turns off automatically when the water reaches a pre-determined heat level. In both cases, the heating process needs to be discontinued. But when there's a fault either in the thermostat or timer or in any other component of the boiler, it might not happen. The boiler keeps on heating the water in any such eventuality, which is not a desirable situation. It may result in:

• Overheating of water that results in excessive heating of rooms and very hot water in the washrooms and kitchens.
• Uncontrolled heating may result in leakage of water.
• It causes waste of fuel, which directly reflects in excessive energy bills.

Reasons and Remedies For a Boiler Running When the Thermostat is Off

If your boiler keeps running while the thermostat or timer is off, you need to inspect and evaluate the entire control gadgets installed on the boiler. The control gadgets generally include thermostats, timers, programmers, and valves. One or more than one of them might have developed a fault, which caused the running of the boiler when the thermostat is turned off.

So, you need to know where the actual fault is. Let’s see what may be the cause and how to fix it.

Faulty Thermostat

A thermostat is a device that is meant for sensing the temperature of the water in the boiler. It has a sensor and a temperature control panel. You can set the temperature level on the control panel of the thermostat, per your requirement. Once the temperature is set to a certain level, the thermostat starts working automatically.

When it senses that the water temperature has dropped from the pre-set level, it turns on the boiler. When the temperature comes to par or crosses the pre-determined level, the thermostat turns off and so does the boiler. But this happens only when the thermostat is functioning perfectly. If a fault occurs in the thermostat, it may not turn off the boiler. Resultantly the boiler keeps on heating the water.

If you observe such an incidence with your boiler, you need to take immediate action to avoid wastage of fuel and overheating of water. Try to change the temperature setting on the thermostat’s control panel. Reduce or increase the temperature level. Turn off and turn on the thermostat manually and see how the boiler responds.

When the temperature level is increased, the boiler should turn on. And if you reduce the temperature level, it should turn off the boiler. See if that works. You can also try to turn off the unit and switch it on again. But if no change occurs in the boiler running, you need to call the boiler engineer to inspect and fix the problem.

Faulty Valves

There are different types of valves fitted on different parts of the boiler. Safety valves are meant to relieve the pressure. When the boiler pressure reaches the danger zone, these valves automatically open and relieve the extra pressure.

But the valves that are directly related to switching a boiler on or off are the diverter valves and the check valves:

• Diverter Valve controls the flow of hot water from the boiler. When the boiler is turned off, the diverter valve closes the water flow from the boiler and allows its flow through the taps.
• The check valve works like a one-way traffic system. It is meant to prevent the backflow of water. It allows the water to flow one-sidedly when opened. It opens when water passes through it but prevents the water to flow backward.

Valves have micro switches in them, which regulate the boiler and pump. When the valve is open, the micro switch gets activated and the boiler and pump start working. When the valve is closed, the micro-switch shuts off the pump and boiler. In case of a fault, the switches remain open, even if the valve is closed. In such an incident, the boiler and pump don't shut off and keep on heating the water.

Another possibility is the jamming of these valves. Due to consistent working, the valves may be damaged or jammed, which results in malfunctioning and the boiler may keep running even when the thermostat is turned off. You may try to release the valves but it needs careful workmanship, as these are too strong and may damage your fingers. Try to do it, if you can, otherwise, you will have to call the boiler technician to fix the problem.

Faulty Timer or Programmer

The timer device controls automatically turning on and turning off the boiler at a fixed time daily. For example, you may set the timer to start at 7 AM and shut down at 7 PM. On the other hand, the programmer can switch on and turn off the boiler at pre-set times on the pre-determined days of the week. The purpose of both these devices is to start and shut down the boiler automatically per the scheduled timings.

Another utility of programming is that it gives you control over the heating and hot water supply at a pre-determined time. It means you can set the time when you want your boiler to provide hot water. Similarly, you can set the schedule of providing heating for the living areas of your home. All this can be controlled with the heat programming device.

But in case the timer develops a fault there may be a possibility that it won’t start or turn off the boiler at the fixed times. When the boiler keeps running even if the timer or programmer is off, it is an indication that these devices may be faulty. You can try to reset the programmer or timer and see the results. Normally, resetting the timer and programmer works well. But in case it doesn’t work, you may need to replace these devices.

Faulty Electric Wiring

Have you checked all the above referred devices and fixed the issues but the boiler is still running? It means that there might be an issue with the electric wiring. If that's the issue, there's hardly anything you can do on your own.

Electric wiring in the boiler is quite a sensitive matter. If you are not familiar with the electric wirings, it is highly recommended not to play with these wires. However, some checks can be performed, if you have a basic knowledge about the electric wiring. First of all, you should turn off the electric supply to the boiler to avoid electric shocks. Then check if some loose connections need to be fixed. You can also check for any damaged or burnt wire. Try replacing it. See if any fuses might have blown. Try to replace them.

But you need to be extra careful while doing any of the above actions. Any mistake in handling these wires may result in damage to the entire boiler system. The best way is to call a qualified boiler engineer to check and fix the issues with the electric wiring.

Conclusion

Boiler performance largely depends on the perfect functioning of its different components such as the thermostat, heat programmer, and valves. Thermostats, timers, and programmers are meant to regulate the functioning of a boiler. The boiler produces hot water. The temperature of this hot water needs to be maintained at a pre-set level. The thermostat regulates and maintains the pre-set temperature by automatically turning on and switching off the boiler.

But often it happens that the thermostat turns off but the boiler keeps on heating the water. Mainly it may be the fault in the thermostat but you cannot rule out the possible fault in other parts of the boiler such as valves and programmer. Electric wiring may also be one of the causes of this type of fault in boilers. If you know the basics of the boiler parts, you may try to resolve the problem on your own. But it is highly recommended to call a qualified boiler engineer to check the problems, especially if there is an issue with the electric wiring.