The Walchem WBL400-545U controller is now obsolete and the closest equivalent is the WBL600 controller. The new WBL600 series has upgraded features; for reference, here is the description of the old model:
Boiler controller - bleed & feed, hardwired, cable glands, single isolated analog (4-20 mA) output, standard electrode (up to 250 psi), integrated datalogging and config file import/export via USB flash stick.