I have a downstairs gas fired system with 8 radiators which has been working fine for a long time. Copper pipe is 22mm "ring" with in/out 15mm feed to each radiator. There was also two "15mm stop-ends" for a 9th radiator which was removed a few years ago.
I have used these two connections to feed 15mm pipe to a new UPSTAIRS towel radiator. While it is now filled with water and fully bled (as are all other radiators) it is not heating up.
There does not appear to be any blockage downstairs at the connection to the former stop-ends but the new 15mm pipe shows very limited heat even 20cm or so away from the 22mm pipe.
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