Pumps don't have automatic valves. What sort of system have you got,
do you have a valve and possibly cylinder stat in the cylinder
cupboard or do you have a gravity system. If the latter it's more than
likely just convection from having the water on.

bog standard gravity fed....

convection could heat most rads in the system then?

don't doubt you at all, but am shocked that they could get so hot
without phsically having water pumped through them...

hmmm, will have to check the temperature setting for the hot water
now, to see if i can turn that down in attempt to cool the rads down..

mind, it's better than freezing i guess, even if the gas bill could be
horrendous