there is water running out of the bottem pipe (overflow) at hte base of my ?

Sounds like the Pressure Relief Valve has actuated.
Usually caused by the shower head being blocked, or the shower hose being compressed during use.
You might find a small ball in your shower area (though it may have gone down the drain), is so this is the fault.
Contact manufacturer for a replavement PRV kit. Relatively easy to replace, but isolate ELECTRICS as well as water before attempting replacement.

DMB
October 2008