The Case of the Short-Cycling Boiler – Causes, Damage & Fixes This weeks video

Thanks for that video, Ray. When I began maintaining the heating system in our 4-unit condo building with 2 Weil-McLain WGO-5 boilers and original gravity-conversion hot water radiators, I realized both boilers were short-cycling.

Your title "Boiler Room Retective" is very apt, because some of the reasons for the short-cycling were not obvious and took some sleuthing. The one that took me longest to figure out was the improper placement of both thermostats. The installer had conveniently run the thermostat wires inside one of the chases where hot water risers go up to the second floor. So of course, the thermostat got installed on the wall right at that chase location. When the heat came on, the riser heated the wall behind the thermostat, causing it to satisfy before the room reached the setpoint temp. That took an IR gun to figure out. The other factors were more obvious.

In the end, we had 4 factors contributing to short cycling:

1. Oversized boilers (4x actual building heat loss at design day temps)
2. Thermostat left on factory default setting for forced hot air, which resulted in too small a differential
3. Thermostat improperly positioned on internally heated wall
4. Draft inside wall blowing air into back of thermostat (fixed by foaming entry hole around Tstat wire)

The hardest problems to solve are the ones where you start with the default assumption that there's only one cause, only to find that you were wrong, and there's actually 2, 3, 4, or more contributing factors. I expect you've seen a lot of those in your career.

Ray Ray does it again! You confirmed, in great detail, all the issues we run in to consulting and redesigning problem heating systems. Your videos are clear, cogent and concise. They are brief and to the point. As an industry, we are grateful to have such a great educator! Mad Dog