Is it normal that radiators become warm when using shower

[daxu]

Hi,
My shower is powered by the gas boiler (not a combi boiler). What I realized is that when I switch the water on for a shower, the radiators become warm even I switched the room thermostat to lowest I can.

My understanding is that the water in the tank need to be heated to provide hot water for the shower. But if I put room thermostat to low, the hot water shouldn't be used to warm up the radiators. Is my understanding right?

Many Thanks

 

[Dan Robinson]

Either a passing zone/midposition valve or reverse circulation.

 

[daxu]

Either a passing zone/midposition valve or reverse circulation.

Thanks, I will check