Is there any convention for which pipe on a hot-water radiator should be the inlet pipe (gets hot first when boiler turns on) and which should be the outlet. I'm thinking in terms of which pipe should have the normal user-control valve (or TRV) and which pipe should have the preset flow-control valve that is used for balancing all the radiators.
Is it simply a case of putting the user/TRV on the end which is more accessible and less likely to be covered by furniture, or is the TRV always on the inlet pipe?