vaillant turbo plus 828E. There is no power to block4 and when I connect power to it the pump comes on and the boiler fires up but only remains on for a minute.

tom hughes, November 2010

First time mis-read No power to 4 = external fault
But:
sounds like you have two problems, if the boiler only fires for a minute with power to 4, watch for diverter valve movement when connecting power to 4 (through the hole on the side of the valve), sounds like the diverter is not opening to the CH side

Carefree, November 2010

No power to terminal block 4 means the fault is external to the boiler ie: Timer/room stat.

The power is fed from the boiler terminal 3, through the external controls and back to terminal 4

Carefree, November 2010