We have a gas fired hot water system... with radiators. We were unable to shut the heater down. We turned down the thermostat... still ran.. the temp went to 80 in the house. The relief value blew and there is 4 inches of water in our basement.

We had a heater man come... he shut everything down and turned off the gas... he is coming back tomorrow.

Could it be the termostat... thanks.

It is possible. However, it could be a number of things. Let the tech do his thing tomorrow and please do let us know what he finds.