Water overflowing radiators

Alden Maddry

I have a 1 pipe steam radiator system in a 5 floor house. I am renovating the house which includes adding a new sunroom and making the cellar into usable space so I need to add heat in those areas. We have replaced the boiler to be a slightly larger size so we can add a new water loop off the steam boiler to heat the new spaces. Currently we are using the top 2 floors but because the lower 3 floors are being renovated the radiators are turned off on those floors. The radiators on the top 2 floors seem to be working ok but when I open any of the radiators on the 1st floor or basement level water starts gushing out. Why would that be? If the radiators on the lower floors of my house are all turned off would that throw off the system and make the water level rise somehow?