My water heaters pressure is building up too high and I can't find a reason why. It blew off a pipe. It isn't the thermostat, It isn't corroded, and the temperature is set low enough.. Any Ideas on what my problem might be and how I can fix it?

Alexis, April 2010

it sounds like the expantion vessel needs checking or
mains water is getting past the filling loop
or heat exchanger

b, April 2010