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I have a 12mm microbore system in my house which has no manifolds. It has 2 circuits and the old radiators have a centre bottom valve which when open lets the water through the radiator when closed loops the water through the valave and on to the next rad. I have fitted on radiator and just put 12mm - 15mm reducer and put 15mm to each end of the rad but if i fit a TVR when it shuts it switches off the whole circuit!! I have thought of just fitting a couple of tees in and a bypass loop but wonder if this will then effect the flow through the radiator. But at least when the TVR closes it will put more heat to the rads further in the circuit one of which never gets hot. This is all fed from a communial boiler which serves the whole estate so i have no boiler to worry about. Help ideas suggestions welcome.

You say you have two circuits but operationally you are describing a single pipe system. What do you mean by two circuits?

If you have a single pipe system (see here https://www.diydoctor.org.uk/projects/ce ... ystems.htm and tell us what you have) there is NO point fitting a TRV (TVR is a car LoL) because exactly what you have described will happen.

Why do you want a TRV on that particular rad?

Is the rad which doesn't heat up the furthest from the boiler?

Cheers

This system has no boiler as it is part of a communal system. It is a single pipe system but where the pipes come into the house it tees off into 2 seperate one pipe circuits. I am guessing the rad that does not get hot is the last in the circuit. Sorry about the typo!!