Furnace indicates a circulation pump fault; no flow through the system, and radiators remain cold.

Safety: Turn off the power. For hydronic systems, allow the system to cool before opening any water components.

• Check pump operation: With power on and a heat demand present, place a screwdriver on the pump body and your ear on the handle to listen for humming or vibration. No sound may indicate a failed motor or a lack of power.
• Bleed air: If the pump has a bleed screw, carefully open it slightly with a cloth ready to catch water. Release trapped air until water flows steadily, then retighten it.
• Free a stuck rotor: With power off, remove the pump's front plug (if present) and gently turn the rotor shaft with a screwdriver to free it. Reinstall the plug and test.
• Inspect strainer: Some IVT systems include a dirt separator or Y-strainer on the return line. Isolate, depressurize, and clean the strainer screen if it is clogged.

If the pump still does not run or trips the breaker, it likely needs replacement by a heating professional.