I believe I have some breed of greenstar junior boiler from worcester bosch. It also has an integral charging link fitted. I have just drained the CH system to install a new towel radiator and wanted to repressurise the system. Unfortunately rather than turning the white control screw to refill the system with water I turned the black screw. Im made a hissing noise which eased after a while and finally came to a stop. I am struggling to find out what this black switch is for. Am I OK to refill and turn on the boiler or do I need to undo whatever it is that I have just done first? Charging link manual https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjtyOb9yrLPAhXoDMAKHWjWDWYQFggcMAA&url=http://www.gotogasdocs.co.uk/f/m/Worcester/Other%20Equipment%20&%20Information/integral-charging-link-fitting-and-user-instructions.pdf&usg=AFQjCNHpEqoPE5BseTqzFnukTIjzfYGQhQ&sig2=GLloH9G-Vos_k6OrE185Yg Boiler manual (i think this is the right one) https://www.worcester-bosch.co.uk/support/document/download/release/6720806709/12644
Insert the key, turn the black or sometimes white knob, the hissing is the water going back into the system, watch the pressure gauge and vent your rads. take it to 1.5 bar and turn off, remove the key
Thanks for the reply Dave. The white knob on the left is the one that allows the water back into the system. The black knob on the right seems to be closely related but is something else. If the black knob was slightly open it leaked when i turned the water back on (White knob). Could be be some kind of bleed valve to let air into the system when you are trying to drain it?
The filling links can be quite tricky to use. need to make sure that the key is inserted correctly then turned to 'unlocked' position. Don't know what the black cap is for but think it only needs to be finger tight. Once the link is unlocked turn the white squarish knob to fill the system.