On the dial the pin was between 0 and 1 (in the red). I turned the pressure valve underneath but it has now gone over to the other side, it's now in between 3 and 4 but still in the red! I have no hot water in the sink and no water coming out of the bath taps! Help!
open the radiator bleed valve to reduce pressure till it in the green, collect water in some kind of pot and dispose. hot water - cannot work if boiler is not at correct setting, no water from bath taps? sounds odd, no water or no HOT water? always try to give as much info as you can, boiler manufacture, model, age, etc. in your case there is a pressure switch which prevents boiler operation if pressure is to high or to low most likely.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix home heating systems.