the tank that feeds the central heating has overflowed.the cold supply ball cock is not leaking.it is not dripping from the overflow but staining suggests water has gushed out.any ideas welcome.thanks
the water is up to overflow level.the ballcock is not leaking.i think the extra water is from the expansion pipe from central heating.the pump is working.the boiler is working.the system has worked fine for years until now.the water is black ,like when the radiators are bled.