Your thermostats on the two radiators my have broken and closed the valves allowing the water through.
If you can try changing the thermostat with another one in the house to see if this is the problem. Or try removing the thermostats temporarily and see whether the valves are closed, if so re-open and then see if the water starts to come through warm.
The only other thing I can think of is that you may have a blockage leading towards the two rads which is effecting the flow of water to them.
If you have British gas protection I'd call them and ask them to check it out.
Hope this helps
Clair
December 2006