You have a bad or open flow check valve.
I have a small old house with a single zone forced hot water heating system. The boiler is a fairly new Dunkirk Empire II oil unit with a coil for hot water. There are two main loops served by one Taco circulator pump.
In the basement, I've noticed that the return pipes in ONE of the two heating loops are very hot for their entire lengths, even though the thermostat is turned all the way down and I'm not calling for heat. All of the supply pipes and the OTHER return loop pipes remain cool to the touch.
If I open the shut-off valves on the radiators that conenct to these warm pipes, I will eventually feel heat from the radiators.
Do these sound like symptoms of a problem I should be concernd about?
I'd hate to be burning more oil than necessary through the summer.
Thanks, John. I'll check this.
Would this cause the boiler to cycle more often?