Boiler cycles on and off rapidly when only one small zone calls for heat.

Safety first: Turn off power before modifying control wiring or settings.

• Step 1 – Confirm zone size: Identify which zone is calling when rapid cycling occurs (e.g., small bathroom loop, towel warmer).
• Step 2 – Adjust boiler settings: If the control allows, lower the boiler’s minimum firing rate or adjust outdoor reset to reduce water temperature during mild weather.
• Step 3 – Combine small zones (pro): A heating contractor may be able to pipe or control small zones so they operate together, increasing load.
• Step 4 – Add buffer tank (pro): Installing a small buffer tank can increase system water volume and reduce cycling.
• Step 5 – Review thermostat cycles per hour: Set thermostats to a lower cycles-per-hour setting if adjustable.

Note: This is a design issue more than a fault; solutions often involve system modifications.