[aerohead]

A guess.The system malfunctions,the house loses heat.Residual moisture condenses and collects in a few of the radiators and fails to drain off.As temperatures fall below freezing temperature inside the house,the water condensate freezes,expands,and ruptures the few radiators.At some point,the system controls sense the ambient house temp and attempts to satify the setback temp setting.The boiler fires,steam emanates from the breach in the shattered radiators,the 100% relative humidity air freezes on the sub-freezing temperature inside surfaces,coating the inside of the house with ice.------------------------- At some point,the logic of the controls "works",and opens a circuit to protect against the malfunction it's just now sensing.Without repairs and a reset from the HVAC technician,the system remains off,maintaining the freezing temps until discovered.