In article ,
Andy Hall wrote:

reverse circulation
------+-------------+---------- CH flow (off)- || --+
RAD RAD |
reverse^circulation V |
| | Pump |
+---A-------------B------------------Boiler --X----MV
| |
CYL |
| |
+----------------------------------O---HW flow ----+


It is better to connect to a common point, as you say. You can get
around the problem with appropriately placed zone valves and that may
be a more practical solution if the CH return pipe is not easily
accessible.

What about just installing one-way valves on both the cylinder return and
new CH return just before the two returns join? That will prevent the HW
return from supplying hot water into the new rads, won't it? Actually the
one-way valve on the cylinder side would not be necessary as it wouldn't
matter if hot water returning from the radiators made its way into the
cylinder coil, would it?

Zane.