HW cylinder has 15mm return - why?

[JC1000]

On moving into our new house I noticed that the return pipe to the boiler from the HW cylinder coil is run in 15mm copper pipe, the supply being in 22mm.

The system seems to have been installed properly in other respects. Any ideas why someone would do that? Am I missing something?

 

[kevplumb]

it resricts the flow

same as using a lockshield on the return

and 15 is cheaper than 22

 

[TicklyT]

Without a restriction on the hot water circuit, all the flow would run through the cylinder when there is a demand for both heating and hot water, leaving you with no heating until the cylinder is up to temperature.

The reason for using 22mm or 28mm cylinder primaries really harks back to when unpumped gravity circulation was the norm.

 

[kirkgas]

you will prob find the vent pipe for the system is connected via the hot water flow so it needs to be in 22mm, the return is done in 15mm as explained by the other posts