Here at Anglo Nordic, we have an extensive selection of boiler thermistors. As our customers have come to expect, each & every one of the products found on this page is of the usual high quality Anglo Nordic demands, coming to us direct from the very best manufacturers.

 

Designed for use with a wide range of boilers. The following boiler thermistors & gas boiler temperature sensors are suitable for use with Ferroli, Baxi, Vaillant, Potterton, Vokera & Worcester, & many more boilers.

 

What is a Thermistor?

With a vital role in your boiler by delivering heat and hot water, thermistors are widely used across a variety of industries. However, have you wondered what a thermistor is exactly?

 

The word thermistor is a combination of the words "thermal" and "resistor". They are made from metals, such as cobalt, nickel, copper and magnesium and is an electrical component which charges with a temperature rise. The metals oxidise via a chemical reaction, are ground to a fine powder and then compressed.

 

Finally they are hit with extreme heat to be encased into a electrical component. One end is left exposed to a heat source, and the other end to an electrical connection.

 

Types of Thermistor - NTC & PTC

There are 2 types of thermistor:

  • Negative Temperature Coefficient (NTC)
  • Positive Temperature Coefficient (PTC)

NTC Thermistors

Put simply, as the temperature rises in NTC thermistors, the resistance drops. These thermistors  work by decreasing the resistance with an increase in temperature. For example 25°C would start at 12,000 Ohms and increase to 55°C while decreasing the Ohms to 4,000.  Usual starting resistances are in the range of 12-15,000 Ohms and can drop as low as 900 Ohms when boiling.

PTC Thermistors

PTC thermistors are the opposite of an NTC, however look the same. They behave differently by increasing the resistance along with the temperature.  The PTCs are less common than NTC thermistor. For example 10° would start at 800 Ohms, and increase up to 90° at 1600 Ohms.

Where to Fit a Boiler Thermistor?

Thermistors are usually located on the flow and return pipes. Either attached on the heat exchanger outlet pipes, in the lower part of the boiler or inside the combustion chamber.

 

Some can be referred to as 'wet' thermistors, as they are in contact with the water to heat. Others are sometimes called 'dry' as they are attached onto a pipe and sense the heat within the pipe. It's also possible for some modern condensers to have a thermistor checking for gas temperatures.

 

How to Control the Temperature

Thermistors are controlled using the potentiometer (the boiler control knobs for temperature), and the Printed Circuit Board (PCB). A direct current is sent to the thermistor via the potentiometer. The PCB knows then whether to increase the heat, or send less gas to to lower temperature. This is done depending on a voltage drop due to the change in current.

 

Further functions of a Thermistor

A thermistor reading is also responsible for telling the boiler when the temperature has fallen too low. This tells the boiler to switch on. This is called an in-built frost protection,this ignites the boiler when the resistance reading drops below a certain point.

 

Thermistors can also be used to monitor an anti scale function, called a pump over-run facility. This is where the pump continues to operate until the temperature has dropped to a set temperature.

 

Testing

A thermistor gives out a resistance reading when it detects a certain temperature. We can test the component’s two connections with a multimeter. Set to read the Ohms, and compare the reading against manufacturers or registered engineer’s charts. We can also do another test to see if the resistance is going up or down correctly as the appliance heats up and is gas safe.

 

Don’t forget to check the leads when testing, as a faulty lead on a thermistor can cause problems. You can do this by testing the leads and thermistor for resistance in one combined test. i.e. instead of disconnecting the leads at the thermistor, measure the resistance across the plug where they join to the Printed Circuit Board (PCB).

 

Temperature Sensors

 

At Anglo Nordic we also offer a range of temperature sensors. Constructed from high quality materials such as hard wearing Adz brass, these temperature sensors offer unbeatable value at excellent prices. Each thermistor has a one year manufacturers warranty & are designed to operate in temperatures ranging between ‑10° to 100° C.

 

Should you require branded packaging, simply contact our customer services team & we will be more than happy to fulfil your request.

 

Anglo Nordic have just what you need! If you have any questions for need more information, simply call us on 0208 979 0988 or email us at sales@anglo-nordic.com.