This flow sensor from the German brand Sika ensures that the circulation pump sends sufficient water into the heater to avoid any risk of overheating. It is found on Elecro heaters in particular.
The VKX05 has a 24 mm internal thread, which is screwed into a heater tee or union. It is designed for a maximum current of 1A.
Internal thread diameter: 24 mm (3/4" FPT)
Reed length: 78,5 mm
Total length: 149 mm
Sika : VKX05M2PSA-04