FRP3 Immersion Temperature Sensors

The FRP3 sensor assembly is commonly found in many gas-fired hot-water boilers.  Through being manufactured in high-volumes, this sensor is relatively low-cost and so can be utilised across a range of temperature sensing applications.

ATC Semitec’s FRP3 sensor is generally supplied with an 1/8″BSPG thread and integral connector, though metric threads and flexible lead-wire options are also readily available.  This sensor can be supplied with various NTC thermistors or with Pt100/Pt1000 platinum elements.

These immersion sensors are available in brass, nickel-plated brass or stainless steel with a typical time constant (Tc) of around 5 seconds.


  • Gas hot water boilers
  • Heating and air conditioning systems
  • Instantaneous hot water heaters
  • Air compressors and diesel generators


  • Fast response design (Tc ≤ 5s)
  • Accuracy ±1%, available ±0.2K (0-70°C)
  • Operating range up to -40°C/ +125°C
  • Interchangeable NTCs or PRTDs
  • Connector or lead-wire options
  • Various housing materials

Technical Specifications

NTC Thermistor Series AT-2, ATC3, ET, GT, ATCS, SP
Temperature Range -40°C/+125°C depending on NTC
Sensor Accuracy R25±3% as standard, ±1% available
Sensor Material Nickel-plated brass, brass, stainless steel
Lead Wires Integral as a special option
Connectors Lumberg 2.5 MSF, Tyco Modu, etc