I'm looking foradvice on how big a job it is to replace a broken radiator valve. I've just moved into a new house and one radiator wasn't working. I thought it just wasn't turned on fully and was a bit stiff, so I used an adjustable wrench to open it (the right hand side valve), but before I'd applied any pressure the valve pin just snapped off. Before I call a plumber I want to get an idea of how big a job this will be? Is it common?