Greenstar 24i or 28i no hot water?

We have no hot water. Our condensation pipe was blocked with ice 2 days ago - no error light flashing, just boiler gurgling and dripping water from joint in condensation pipe just below boiler but heating was working ok and so was hot water. We switched off boiler at the on/ off button (due to gurgling sound). Unblocked ice in pipe and switched on boiler again and heating ok and dripping stopped. BUT since this happened we have no hot water. The boiler seems to fire up when hot water tap is switched on and a green '?gas?' light indicator comes on. It even makes a slight click/clunk. The water comes out hot for a few seconds then goes freezing cold. We have tried switching power off and boiler and switching back on. Tried pressing reset button but still no hot water. Can you help please?

Bev Mc
December 2010