Rads heating (a bit) with UFH

[Simarwood]

Hi, we have a completely new install from scratch/building site.

When UFH zone comes on, some of the rads also come on a bit. The same also happens when the hot water comes on. They are operated separately though

Is this normal, or is something wrong (and is it a big deal?). I worry I am losing efficiency in UFH zone.

Looking for a fix!

 

[Ben-gee]

Most likely the order in which the returns have been joined together on their way back to the boiler.
Sounds like your system has got it wrong so there is leaching into the rads- more irritating than a real problem - but incorrectly set up. (This is my guess anyway)

 

[exedon2]

Pic of your zone valve / underfloor manifold set up would be useful.
As Ben-gee as indicated may be a problem with way returns are connected the return from cylinder must always be last connection.