Dual heating system with upstairs and down stairs thermostats

[Stupidstu]

Hi I have a dual heating system ie separate thermostats for upstairs and down stairs, my question is why does my upstairs bathroom radiator come one when I turn my downstairs heating on ??

Surely this should come on when I put the upstairs on ??

 

[king of pipes]

Possibly piped wrong ? , but could also be it's connected to the primary circuit so when the hot water is called for the towel rail or rails get hot ? often done like this for summer use when the heating is set to off and not needed , to dry towels

 

[Stupidstu]

Possibly piped wrong ? , but could also be it's connected to the primary circuit so when the hot water is called for the towel rail or rails get hot ? often done like this for summer use when the heating is set to off and not needed , to dry towels

I’d understand that if it had towel rail but just a normal radiator lol I’m going for piped wrong as it’s a new build

 

[king of pipes]

I’d understand that if it had towel rail but just a normal radiator lol I’m going for piped wrong as it’s a new build

Think your probably right