"Set Square" wrote in
:


The only satisfactory cure is to convert from a Y-Plan to an S-Plan by
throwing away the 3-port valve and replacing it with two 2-port
valves. This removes a major single point of failure from the system.
It's not too difficult to do, provided you can get at the pipe runs
immediately after the 3-port valve, inserting a 2-port valve in each
leg, and replacing the 3-port valve with an ordinary tee. If your
system is vented, with the vent pipe connected near the HW cylinder,
the HW zone valve needs to be inserted close to the cylinder, *after*
the vent pipe connection in order to ensure that there is always a
clear path from boiler to vent, with no valves in the way. If your
boiler has a pump over-run stat, you'll also need a by-pass circuit -
to give the water somewhere to go when the pump is running with both
valves closed. An automatic by-pass valve between flow and return,
connected after the pump but before the zone valves, is best.

I'm proposing to do just that SS, but could you suggest a good valve - in
particular I'm looking for minimum constriction (my existing 3port valve
has diddy holes for the coolant (heatant?)

mike