Yes, you should be able to manually unscrew the cap about 1/2 turn to manually vent the air. When closed, the hygroscopic discs will automatically bleed air (if the discs are not clogged). If the knob will not turn it is probably stuck due to excessive lime scale buildup. We suggest replacing it with a Caleffi 5080.
Yes, you should be able to manually unscrew the cap about 1/2 turn to manually vent the air. When closed, the hygroscopic discs will automatically bleed air (if the discs are not clogged). If the knob will not turn it is probably stuck due to excessive lime scale buildup. We suggest replacing it with a Caleffi 5080.