Gas burner control unit IFS 137 B-3 Kromschroeder
Automatic gas firing devices IFS 137 B, similar to IFS 135, but the
ignition valve remains open for half a safety delay if the flame goes
off during operation, DIN-DVGW approval
sec. A = Start safety delay
sec. B/H = main gas/operation safety delay
sec. B/Z = ignition gas/operation safety delay
