Each cycle costs a purge that cools the boiler, an ignition sequence that wears igniters and valves, and minutes of inefficient warm-up, and non-condensing boilers condense flue gas during each cold start. Common causes are an oversized boiler, a narrow control differential, small zones calling alone, too little turndown, or a misplaced sensor. Fixes include right-sizing, wider differentials, buffer tanks and outdoor reset.
Boiler's short cycling, eight starts an hour on a mild day, it's double the size of the heat loss.
Count burner starts per hour from the controller history; more than six on a mild day is a red flag.
Also heard as
- short-cycling
- rapid cycling
Related terms
Turndown
The ratio of a burner's highest to lowest firing rate, such as 4 to 1 or 10 to 1.
Differential
The gap between the point where a control turns the burner on and the point where it turns it off.
MBH
Thousands of Btu per hour: the everyday unit for rating heating boilers, burners and heating loads.
Outdoor reset
A control strategy that lowers hot water supply temperature as outdoor temperature rises, following a set curve.