Radiators upstairs will not go off after relighting Potterton Kingfisher ?

Hi,

I have an old Potterton Kingfisher CF50 boiler.
Yesterday we had no hot water so re-lit the pilot light but the boiler did not fire up. When we switched the switch underneath the timer (thought to be purely for heating?) the boiler fired up & then produced hot water.

However, the radiators upstairs are now on & will not turn off even though the switch (thought to be for heating) is off. The radiators upstairs are boiling but downstairs completely cold.

Could this be something to do with the timer? My husbands grandfather fiddled with it but I thought it was broken so did not really pay any attention.

Please help as it is sooo hot & I dread to think how much it is costing!!