Sit Gas valve 843 SIGMA 0.843.003

The Sit Gas valve 843 SIGMA 0.843.003 is an electromechanical safety and metering device installed in the gas supply line between the gas filter and the burner. It opens only when the burner control sends a voltage signal and the gas pressure switch confirms that the inlet pressure is within the acceptable range. This valve is designed for Protherm boilers with models 20...60 KLO-13 and is an OEM equivalent to part number 0020025299. It operates as a single- or double-solenoid, slow-opening, servo-regulated unit, potentially incorporating a gas filter and pressure regulator in one body.

When selecting a replacement gas valve of this type, key parameters to match include the brand and series, connection size (typically Rp 1/2" to 2" female threaded or flanged), coil supply voltage (common values are 230 V AC or 24 V AC/DC), and internal function—whether it is a simple on/off valve, modulating valve, or combination with a built-in regulator. The coil is normally interchangeable with other coils of the same voltage from the same series, allowing quick repair without removing the valve body. Before ordering, verify that the new unit matches the existing gas pressure switch settings and the burner control output, and ensure connection threads or flange gaskets are in good condition to avoid leaks.

Common service issues for valves of this type include coil burnout (check resistance and insulation), a leaking seat causing gas to pass in the closed position, drifting outlet pressure due to a worn servo regulator diaphragm or spring, and a seized servo mechanism from contamination or corrosion. When these failures occur, the equipment may fail to ignite, exhibit unstable flame, or show pressure fluctuations. Check the coil resistance and insulation, inspect the seat for leaks, and examine the servo components for wear or blockage.