Short cycling hydronic boiler

RayWohlfarth

Why is my hydronic boiler short cycling? This week's video.

It talks about how to recognize and solve short cycling on a hydronic boiler.

https://www.youtube.com/watch?v=BKmUoWc5pCs

EdTheHeaterMan

Great Video Ray

There is one that I discovered early in my career that I wish to share. The illusive Taco 570 series zone valves and the older heat anticipators that were a resistance heater like the T87F and the T822D models. The amperage draw on those heat motors are between 0.9 and 1.0 amps. This will over heat that anticipator and satisfy the thermostat in very short order, like within a minute. Then cool off just as fast. You can get a thermostat to cycle 50 to 90 times per hour on a long call for heat. It was a real eye opener for me when I went on a service where someone just replaced the thermostat and the house would not get up to temperature. The oil burner actually was turning off after operating for less than one minute.

This was a real stumper for me, but I was a rookie back in the day. After using all I learned in technical school on how to use a meter to determine what circuit was opening to cause the burner to stop, I narrowed it down to the new thermostat. So I replaced it with another T87F and got the same result. (read my signature tag line below). I called the service manager and he told me to check the heat anticipator the way I was taught using my amp meter with the 10 wraps of wire around the probe clamp. It said the heat anticipator should be set at 9.6, or actually .96 since I needed to divide by 10. The T87F was factory set at about 0.32 amp. I slid the anticipator arrow to the 0.9ish area which is close to the end on the dial and all was good. Those Taco zone valves are real power users. and there are still some in use, connected to T87F thermostats. I looked at the copper winding of the heat anticipator and saw that is was really discoloured from overheating. Go figure.

Now a replacement thermostat probably will not have that antique heat anticipator for the most part, but there may be some out there and reading this post may bring a rookie to the head of the class if they solve it with a slight adjustment.

Thanks for the video Ray.

RayWohlfarth

Thanks @EdTheHeaterMan Thats a great story. Have a good weekend