TheScullster wrote:
Hi all

I am getting very slow heat up of rads to an extension over the garage
(my/our bedroom as it turns out).
Tried turning down all the lockshields to encourage flow upstairs etc.
But, to get any real heat at all to these, the lock shields have to be so
closed down that the heat up time generally is ridiculous and the rads don't
get warm over their entire surface.
So, I believe that the supply to the upstairs (15mm) is undersize for the
number/size of rads, pipe lengths etc.- 6 rads single convector (average 1m
long 600 high) and 1 towel rail 500 wide x 1800 high approx.
The system is S plan and if I turn the pump speed up, I get pump over.
Maybe it's easier to pump over than overcome the throttled down valves and
the smaller 15mm piping.

So the question is - should I go plastic for the larger 22mm pipe and
replace existing copper?
If so, I understand that this shouldn't go right up to the boiler. If not
how close?

Thanks for any comments on above.

Phil

On my 17KW oil boiler the install instructions said not to use plastic
within 1 metre of the boiler.

The figures I have for pipe sizing says 22mm is used for 5.5-11KW of
heat. 15mm would be for 2.1-5.5KW. So you need to add up the heat
output for your radiators you are feeding with that pipe. I know too
big a pipe means the water runs too slowly and you can sludge up the
pipes. I don't have the details to hand for that right now.