Should these be fitted to the flow, the return, or does it not really matter? The idea being that until the valve opens there is no circulation, no matter if the valve is at the start, middle or end of the loop.
Convention seems to have them on the flow, but I'm thinking that because the temperatures on the return will be lower, putting them there will protect the delicate little insides a bit more.
Worth worrying about, or should I just go with the flow?