Special Offer Pack of 2 - XL Bayliss Vent Openers
This Bayliss XL is an extremely reliable automatic vent opener, made here in the UK.
The opener is activated by a stainless steel cylinder containing a mineral wax which expands with heat; this pushes a piston causing the vent to open. As the temperature falls the wax contracts and a strong stainless steel spring closes the opener.