Heating pipework

[Mercedes7Astra]

Since I last made contact I have had the radiators removed and manually flushed through, whilst talking to the engineer I questioned the fact that the pipework runs from 8mm to 15 mm particularly downstairs, does this cause a problem with flow thus causing the radiaitors not to get fully hot, the engineer says the change in 8mm to 15mm won't make any difference to the flow of water to the rads is this correct. I would have thought that the 15mm would slow down the flow?.

Any comments
Thanks

 

[Agile]

Any significant length of 8 mm will slow the flow down.

The evidence of this will be that the flow into the rad will be hot and the return more than 20° cooler.

Without seeing all your system its difficult for me to give much advice.

8 mm only needs a very small abount of dirt to make a big difference to the flow rate!

Tony