In an earlier contribution to this discussion,
Tim Kedwards wrote:

Hello !

Majority of radiators are fed through 8mm "micro-pore" copper pipes

Blimey, I hope not!! Micro-BORE more like. (You don't really want them to
*breathe*, do you?!)


A couple of the radiators do not get as hot as others despite having
balanced the system. So if I feel the 8mm pipe (to what I think is)
feeding the radiator it is too hot to touch for too long but the
return valve pipe at the opposite end is considerably cooler. I have
opened both the return and flow valves to their maximum flow but this
temp differential still remains and the radiator does get hot but not
as hot as some others.

What sized radiators (in terms of their rated heat output) are they? Does
each radiator have an individual 8mm feed and return pipe, connected back
into something bigger - or is a single 8mm feed shared by more than one rad?
[There's a finite limit to how much heat you can reasonably carry through
8mm pipe. I forget exactly what it is, but it's in the region of 1.5 - 2 kW]

What happens if you turn all the other rads off - do the 2 cool ones get hot
then? If so, you still have a balancing problem. Is your pump running on its
maximum setting? If not, turn it up a notch and rebalance. It it's already
at max, or if these rads are too big for 8mm pipe anyway, you may need to
increase the pipe size.


One other quick question - surely when trying to determine which is
the inlet and return end of a radiator - if one of the radiator feed
pipes is very much hotter than the other this would indicate that it
is the inflow. The reason I ask is that all the downstairs rads have
an integrated bleed valve on one side (which I took as being the
return side). But I have found that this side produces consistently
hotter feed pipes which to my small brain indicates that they are the
inflow

It doesn't matter which side the bleed valve is. Integrated ones are often
on the right - but which side is feed and which is return is usually
determined by which is more convenient from a plumbing point of view. The
bleed valve simply lets air at at the highest point, regardless of water
flow direction. Your assumption is right about the feed pipe being hotter
than the return pipe.
--
Cheers,
Set Square
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