if its a combi and the cold water pressure is ok then there is usually a filter on the cold feed into the boiler , this will not be visable and will need nuts undoing to find it , follow the cold pipe into the bottom of the boiler and it will be there somewhere it will not be actually inside the boiler it is always on the pipe into it , I am assuming that the valve on the inlet pipe into the boiler is fully open as well
Steve
February 2005