/diy/ - Do It Yourself

>>2782013
In theory there is less pressure in the radiator than the pipe inbetween, so water flows mostly through it when the thermostat is open. When it can't flow through the radiator the hot water circulates in the pipes only.
In practice it doesn't work properly, even more advanced systems with proper bypasses are bad. Systems with 2 separate pipes are always much better but were marginally more expensive.