Kromschroder Air/gas ratio control VAG125R/NWAK 88000349

The Kromschroder VAG125R/NWAK is a combined gas/air pressure regulator and solenoid valve for burner systems. It automatically meters gas flow in proportion to fan-delivered combustion air, keeping the gas/air ratio stable over the firing range. The valve has a nominal diameter of 25 mm with an Rp 1 internal thread, runs on 230 V AC at 50–60 Hz, and is rated IP65. Its valve and regulator are class A, and the mechanism opens and closes fast to minimize delays when operating conditions change.

For air/gas ratio controls of this kind, replacement selection starts by comparing the pipe connection (threaded Rp 1/2” to 2” or flanged) and the coil voltage (230 V AC or 24 V AC/DC) with the existing system. The pneumatic impulse line—often marked 'nwak'—must be connected to the fan pressure tap; if the wrong tap is used or the line is blocked, the burner will not modulate correctly. Before fitting, also confirm the pressure switch setting against the manufacturer's instructions.

Typical failures of these controls include a leaking servo diaphragm, a seized adjustment spindle, and a faulty solenoid coil. The burner may then show unstable gas/air ratio, fail to modulate, or run rich with elevated CO. Check the diaphragm for leaks, rotate the spindle through its range, and verify coil continuity. Also inspect the impulse line for blockages or leaks.