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

Hi Ray, love your videos and info.

Funny this topic came up. I generally heat either wood but it’s been so cold in New Hampshire this seasonI’ve had to turn on my Modine heater in the garage.

There’s aquastat control on the modine in the garage itself, but I feel like my boil is constantly cycling to heat this. My boil is probably oversized especially since now I only use it basically for the garage when extreme cold and for hot water. I feel like when the garage it’s calling for heat after the reserves are used up I would think my would start and then run just about constantly until the temperature is reached. Because I’m generally bringing it from 40 up to 55. And then trying to maintain 55. It amazes me how fast after the modine starts up how fast it blowing almost cool air before it shuts off and the cycle starts up again. I feel like if boiler just ran, it should be able to keep up..

Do you have any suggestions? Let me know and thanks again for doing what you do.

Kevin

@jesmed1

That is the hardest thing. I think our brains are set up to think and analyze like it is one problem when it may be 2 or 3.

I have gone down that road many times. Its easy to get lost in the clouds or go down the wrong track. Sometimes I have started at the other end…….cross off the things that are working and the things it can't be first