Furnace starts but shuts down after a few minutes without showing an error code; house does not reach set temperature.

Safety first: Turn off power before accessing wiring or sensors.

• Check filters and vents: Ensure air filters (if present) and vents are clean and unobstructed.
• Verify thermostat operation: Bypass the room thermostat temporarily (link call‑for‑heat terminals) to see if the furnace runs longer. Restore wiring afterward.
• Inspect sensors: Ensure flow and return sensors are firmly attached to pipes and not loose or poorly insulated.
• Call technician: If shutdowns persist, a professional should check pump performance, safety devices, and control parameters.