We have a bedroom radiator that we occasionally want to turn right down. It has 'tamper-proof' caps on the valves at each end. So I will replace one cap with a new one that easily allows the turning of the valve.
Is it advisable to put the new cap on either the water incoming end or the water outgoing end of the radiator?
That can mean it's the bypass loop for the system, so you can't turn it down. You can reduce its output by partially or fully covering it with towels or similar.
Otherwise, you will first have to show it isn't the bypass loop for the system.
Is the system's thermostat in the same room? If so turn that down. If that makes the rest of the house too cold, use the towel method aa20s above.
BTW, doesn't matter which end the flow is controlled from. Some early TRVs did care which way the water flows through them, but I don't think any current ones do.
Why not go for TRV?
I would put the adjusting valve at the most convenient end for its intended use.
It makes little difference so put it on the side where it is more convenient.
Have you soured a suitable wheel-head cap yet, they are not as easy as you might think to find, and the spindle size varies. This site might be useful
It is probably a heat sink and has these valves fitted so it can't be turned off. Really you shouldn't mess with it.
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