ok swaped the old gravity fed cylinder for a Range presurised cylinder. the hot and cold work brilliantly now , but the flow from the boiler is not going round the primary coil. it is piped up exactly the same as it was in the old cylinder (all i had to do was extend the pipes by about 10 inch) the hot flow gets to the inlet side of the cylinder, but the outlet pipe doesnt get warm. is there a chance the system needs a better pump because the new cylinder has twice as much primary coil? or is there another answer. the boiler is an IDEAL Classic. i thought that it would just be a straight swap, cant really understand it