flow and return

[zooankski]

Plumber finished installing a Joule 250ltr horizontal cylinder in my eves space. Water is hot and it appears to be working.
I noticed while I was insulating the pipe work that the return is 10 degrees hotter than the flow (water 2 way valve oil closed at the moment and I left 2 small thermometers on each pipe over night)
I would assume the flow should be hotter? or would that only be the case when 2 port valve opens and boiler fires?
Can flow and return only be checked when water heating is being demanded and then check pipe temperatures?

 

[oilhead]

Are you sure you are looking at the pipes properly? Unless you have a heat source independent of the boiler, the condition you describe is a physical impossibility, or your plumber has discovered the energy equivalent of perpetual motion.

 

[45yearsagasman]

Check flow temps when boiler is heating the cylinder is the correct way.

 

[Madrab]

Physically impossible, has to be the other way about. Is the cylinder marked flow and return, if so they must be fitted the opposite way around. Will it make a huge difference .... depends on the coil really and that the 2port valve and other key components are all in their relative locations. Was he qualified (UHW/G3) to install an unvented?