TRV's and Lockshields which way round

I put the TRV on the outlet/return on the basis that the pipe is cooler and would interfere with the TRV's operation less. Make sure the TRV supports the direction of flow you will be using (I think most are bidirectional nowadays, but they didn't used to be).

Inlet/flow heats up first.

Are you sure you mean TRVs (thermostatic valves) - 'cos they don't generally look like lockshields?

Ordinary hand-operated valves often have the same working parts as lockshields, with only the rotating handwheel or non-rotating cap distinguishing them. In fact, some are supplied with two tops, and can be used as either depending on which top you use. But TRVs have large-ish detachable capsules containing the thermostatic element, and the 'wet' part of the valve is operated by a pin which moves up and down rather than by rotating the shaft.

To come back to your question, the usual convention seems to be to have the lockshield on the return side of the rad, but it doesn't really matter - it will work either way round. However, if you *are* using TRVs, and if they are directional (as some but not all are) make sure that the flow goes the right way through them or they may not work properly, and will probably be noisy.

No sorry my message wasnt clear I didnt mean that the rads originally have TRV's they currently have lockshields and normal valves, oh and as for working out which direction the water flows I was having a blonde moment

In theory. For reasons I have yet to figure out the temperatures of the pipes on our bathroom radiator swap around depending on if the boiler is firing or not. This is a fully pumped system and the pump is running all the time...

In message , Olly writes

If I'm fitting bi-directional flow TRVs they go on the side of the radiator that is easiest to reach to adjust, normally, but not always this is the right hand side, as I'm right handed.