Temperature Controls

Temperature controls are devices that control the operating temperature of the boiler. Hot water boilers typically operate off of temperature. Some of these controllers are also safety devices that make sure that you do not go above a certain set point and will shut down your boiler/burner in cases where you exceed that set point. Brands such as Honeywell, Dwyer, Siemens, Johnson Controls, Ashcroft are common and we stock a wide range of those brands.

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Boiler Temperature Controls

Temperature Controls Categories

What are Temperature Controls & what is their function?

Temperature Controls keep boilers operating in spec

Boilers are all about converting heat into steam. In order to do that in the safest and most efficient way, they require temperature controls that can adjust the boiler’s water or heat level as needed. That way, the entire combustion-to-steam-to-condensate cycle can be kept in proper balance for optimal performance.

Different Types of Temperature Controls & How to Choose

Temperature controls fall into two categories: mechanical aquastats, and electronic loop controllers. 


Aquastats are mechanical sensors that rely on physics to operate. Every aquastat has a high limit and a low limit. If the temperature in an operating boiler is below the low limit, the boiler will fire. If the temperature inside the boiler reaches or exceeds the high limit, the aquastat will cut off combustion to prevent the boiler from overheating.

Loop Controllers

Loop controllers use electronic sensors to detect the temperatures inside a boiler. These sensors convert heat into an electronic signal. As the heat increases or decreases, the electronic signal sent to the boiler controller will change. Based on this signal, the control system will know the temperatures, and whether the boiler needs to fire, continue firing, or stop firing.

The Role Temperature Controls Play in a Boiler

Temperature controls preserve safety, efficiency, and longevity by keeping the boiler operating within specified temperatures. If the boiler were to run too hot, it shortens the life of the boiler by stressing the metal components. Over time, this stress can lead to warping, cracking, or even an explosion. If the boiler is allowed to run too cool, it will not produce enough usable steam to meet demand. 

what is the Effect of a Bad Temperature Control?

When a temperature control starts to go bad, it may give inaccurate readings, or fail to cut off or increase boiler firing based on demand. This can cause a loss of steam pressure, increased steam pressure, or elevated or lowered stack temperatures. 

Things to Consider about temperature controls:

  • Because of their precision and constant feedback signal, loop controllers allow for greater efficiency — especially when installed in a system with electronically modulated valves.

Helpful Resources

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Explore over 750+ explanatory videos on boilers and boiler systems on our Youtube channel. Our videos can help you quickly grasp complex boiler topics. Watch more here!

Relevant WARE Blog Articles on Temperature Controls

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Technical Documents

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Formulas and Measurements

Temperature Controls FAQ

How do I know if my temperature control valve is operating properly?

Always check your stack temperatures regularly. If they’re consistently higher than normal, have your temperature controls checked to make sure they’re operating properly. 

How can I tell if I have an aquastat or a loop controller?

Aquastats are purely mechanical. They will have a dial and a mechanical linkage to the boiler’s control system. Loop controllers, on the other hand, use sensors and electrical wiring to maintain communication with the boiler control system.