Safety temperature limiter

A safety temperature limiter (STB) is a component that interrupts the heating process of a heat generator when a previously set maximum permissible temperature is reached (temperature limit value). This also applies if the connection pipe breaks or if there is a leak in the sensor system. A spring accumulator then closes a valve that interrupts the flow of the heat transfer medium . This protects the heat generator itself, or a system connected to it, from destruction. Accordingly, the STB only becomes effective if the temperature controller fails. The highest switching point of the temperature controller must be a certain distance from the switching point of the STB.

The heating process can only be continued by manually switching the safety temperature limiter back on, often using a special tool. However, this only applies if the fault has been eliminated and the temperature has fallen below the limit value.

As a rule, the STB is also preceded by a safety temperature monitor (STW) or temperature controller (TR). Its temperature threshold is approx. 5 to 10 Kelvin below the threshold of the STB. These sensors enable the system again without manual intervention after the temperature falls below the set temperature. In practice, poorly configured control of boiler systems can lead to the boiler being deactivated via the TR instead of being controlled. Due to the increased switching frequency of the boiler, this leads to additional consumption costs. There is also the possibility that when a gas boiler is switched off at full load, parts of the burner are damaged or even destroyed.

In fully automatic coffee machines and portafilter machines, the safety temperature limiter is intended to prevent uncontrolled heating in the event of a malfunction in the temperature control in the kettles. Otherwise a boiler explosion could occur without an STB.

DIN EN 12828 defines the performance range from which a safety temperature limiter is required. Basically, a distinction can be made between "directly" and "indirectly" fired heat generators.

Common areas of application for safety temperature limiters:

• Boiler systems
• Combined heat and power plants (CHP)
• Heat exchanger

• closed heating systems , underfloor and collector heating

• electrically and gas-heated instantaneous water heaters
• Coffee and steam boilers in coffee machines and portafilter machines

Safety equipment for heat generation systems (DIN EN 12828)