How can I tell which pipe is flow or return

[Cat007077]

Hi,
total novice … im renovating my deceased pop‘s house … the central heating has been drained and radiators removed (not by me). I want to add two new radiators to the system in two bedrooms that never had any fitted and a towel radiator in the bathroom. The pipe work for all the other radiators are in place. However, how would I know which pipe from combi boiler is flow or return? There is no water (obvs in the system to see which gets hottest etc.
any advice would be most welcome

 

[ianmcd]

Doesent matter just make sure you buy bi-directional TRV s

 

[Cat007077]

Thanks for your prompt reply

All rads are connected to two 22mm pipes that go to 15mm. Then microbios… can I just tap into 15mm or 22mm?

 

[ianmcd]

Thanks for your prompt reply

All rads are connected to two 22mm pipes that go to 15mm. Then microbios… can I just tap into 15mm or 22mm?

No tap into the 22mm