Furnace frequently short cycles, turning on and off rapidly without maintaining a stable room temperature.

Safety first: Turn off power before accessing control wiring.

• Check thermostat location: Ensure the room thermostat is not near heat sources, direct sunlight, or drafts. Relocate if necessary.
• Verify thermostat settings: Set appropriate temperature and cycle rate (if adjustable). Replace batteries in wireless thermostats.
• System balancing: Partially close lockshield valves on radiators that heat too quickly to encourage more even distribution.
• Consult technician: If the furnace is significantly oversized or modulation is not configured correctly, a Sime technician can adjust parameters or recommend system changes.