Plastic CH Pipe - How Close to Boiler

[TheScullster]

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

[Christian McArdle]

What is the boiler? You might want to consider switching to sealed pressurised operation, which eliminates pump over and allows higher pump speeds.

Probably. You may find you need to fix the pumping over at high pump speeds even then. However, 15mm does sound very marginal for the load and 22mm is probably more realistic.

2-3m or so, although you should specifically check the instructions of both the boiler and the pipe manufacturer and use the largest figure you find in either. It's more of an issue on older non-condensing boilers.

Christian.

[rjc4687]

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.