element in side will have broken , none repairable part
will need replacing.u can still turn them off by vavle on op/side ,unscrew the screw on top of this vavle take off plastic cover turn off with plyers.as 4 one that will not come on take top of thermo vavle ,u will see pin in middle of part left on rad oil tap lightly until it pops up
some times they get stuck
pete
December 2008