COULD VERY WELL BE AS THE WATER STILL IN YOUR HEATING SYSTEM WILL EXPAND CAUSING A GREATER PRESSURE IN YOUR HEATING SYSTEM WHEN HEATED UP FIRST CHECK AROUND ALL YOUR RADIATOR VALVES IF NO SIGNS OF A LEAK ARE PRESENT GO OUTSIDE AND THERE SHOULD BE A PIPE PROTRUDING OUT OF THE WALL BEHIND THE BOILER CHECK FOR SIGNS OF WATER IE WATER LINES DOWN WALL , MELTED SNOW, IF THERE IS YOU FIRST NEED TO REPLACE THE PRESSURE RELIEF VALVE, THIS SHOULD SORT PROBLEM IF NOT THEN YOU HAVE A PROBLEM CAUSING THE PRESSURE RELIEF TO BLOW OFF
MIKE
December 2005