Determining the last radiator in the downstairs radiator run

[elmocambo]

I am attempting to find out which one is the last radiator by using a DMM connected to a themocouple. All the valves are completely open.
(The floor is solid concrete)
However they all seem to heat up simultaneously more or less.
The reason for doing this is that a wish to add a radiator or two to a garage conversion
Is there another way of doing this?

 

[Chuck]

It's better, IME, to attach the thermocouple to the pipe providing the flow not the body of the radiator. Another trick is to reduce the pump speed so everything happens slower. You might be able to trace the paths using a thermal camera. If you don't have one they can be rented (or employ a heating engineer who has one on the van).