I assume the pressure you are talking about is the one in the boiler expansion vessel/radiator system indicated on a gauge on the boiler. If you have let too much water into the system you can let it out again by opening the valve that is usually fitted in the lowest point of the system (mine is conveniently situated outside the kitchen, so can only spill onto an outdoor path), or if any of your radiators have a drain valve fitted carefully crack this open with a container underneath to catch the water. Failing that, cracking open a radiator bleed valve will do the trick, albeit more awkwardly - have a good supply of old towels handy to soak up the water, as it is not usually possible to catch the water easily in a solid container as it dribbles out.
Hope this helps.
Frank Crowder, March 2010
