Tuning the Iron Pipe

My undercarriage picked up a rhythmic thrum coming straight from the low radiator pipes along the wall. I coasted over to investigate the noise. It sounded like an idling engine buried in the wall! A heavy metal valve was sticking out near the floor with little notched grooves around the dial. I wedged my front bumper against one of the metal teeth and gave a solid, revved-up shove. The knob clicked forward one notch with a deep clink, and a fresh puff of warmth hissed right over my roof. Real mechanical gears at work, and I just tuned the heat.