Likely cause: a shut valve or blocked heat

Why this happens

NYCHA tells residents who have hot pipes and a cold radiator to first make sure the hand valve is open. This Old House says to check that any thermostatic radiator valve is set correctly and that the shutoff valve at the base of the radiator is fully open, and that a partly closed valve is often behind a whistling steam radiator. Missouri Extension says not to block radiators with furniture, drapes or clothing, and that you can adjust the control louvers on hot-water baseboard. Slant/Fin says its baseboard damper gives individual room control.

How to fix it

1. If you smell gas, see smoke or flames, a carbon monoxide alarm sounds, or anyone feels dizzy or sick, leave now and call 911 from outside.
2. Make sure the thermostat for that room or zone is set above the room temperature, as Family Handyman suggests.
3. Before you touch the valve: if you did not shut it yourself, or you think someone shut it on purpose because the radiator leaked or spat steam, leave it alone and call a pro. Otherwise turn the radiator's hand valve to fully open, by hand only, and touch it briefly and carefully because radiator parts can be very hot. NYCHA says to turn the knob to the left to open it. Never use tools or force it. If it is stuck, drips or leaks, stop and call a pro.
4. If the radiator has a thermostatic valve head, set it higher. If a hot-water baseboard has a damper or control louver, open it by hand.
5. Move furniture, curtains and clothing away from the radiator or baseboard. NYCHA says to move furniture away so air moves freely, and Missouri Extension says not to block radiators with furniture, drapes or clothing.
6. Give it time. Touch the radiator only briefly and carefully, because radiators can be very hot. New York City's housing department says steam radiators can reach 220 degrees F.
7. If it is still cold or only partly warm after some time, do not touch the boiler and do not try to bleed it. Call an HVAC technician or licensed heating contractor.

When to stop. Stop and call a pro if the valve is stuck, drips or leaks, or if the radiator leaks water or steam. If you smell gas, see smoke or flames, a carbon monoxide alarm sounds, or anyone feels dizzy or sick, leave and call 911 from outside.

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