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Radiator not working in Brooklyn? Why one stays cold

If the boiler is running and most rooms are warm but one radiator stays cold, the problem is usually that radiator, its valve, or its air vent, not the whole system. First work out what kind of system you have.

Renting? Heat is your landlord's job, not yours. Tell your landlord or super first (in writing, like a text or email, so you have a record). If it isn't fixed, file a complaint with 311 (call 311, use the 311 app or 311 online), and HPD can send an inspector. Don't pay a contractor to fix your building's heat. Our matching is for homeowners, co-op/condo owners and landlords.

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Emergency? Gas smell, CO alarm, fire, sparking or flooding: get to safety and call 911 first.

Steam or hot water?

One-pipe steam (very common in Brooklyn row houses and pre-war buildings) has one pipe going into each radiator and a small metal air vent on the side. Two-pipe steam has two pipes and usually a trap where the return pipe leaves the radiator. Hot-water (hydronic) radiators have two pipes and a small bleed screw near the top, and the boiler shows a pressure gauge instead of a water sight glass.

Why a steam radiator stays cold

  • Clogged or painted-over air vent: steam can't get in until the air gets out. A stuck vent means a cold radiator.
  • Valve half-closed: one-pipe steam valves should be fully open or fully closed. Half-open causes problems.
  • Wrong pitch: a one-pipe radiator should tilt slightly toward its valve so water can drain back. Water trapped inside blocks steam (and causes banging).
  • Failed trap on two-pipe systems.
  • System balance: radiators far from the boiler heat last, and main line vents in the basement matter too.

Why a hot-water radiator stays cold

Usually trapped air. Others are a closed valve, low system pressure, a failing circulator pump or a zone valve that's stuck.

What you can check yourself

  1. Make sure the valve is fully open (for one-pipe steam, all the way).
  2. Make sure the air vent isn't painted over or blocked by furniture or a cover.
  3. With the heat off and the radiator cool, put a level on top. A one-pipe radiator should lean slightly toward the valve.
  4. For hot water only: bleed the radiator with a radiator key and a towel, and stop when water comes out. Don't try to “bleed” a steam radiator.

What a pro typically does

Replace the air vent or trap, re-pitch the radiator with shims, clean or replace valves, check main vents, and balance the system. Leaking valves or radiators that need to be moved should go to a licensed plumber. Costs depend on what's wrong and how many radiators are involved, so get a quote first.

Questions

Can I replace a steam radiator air vent myself?

On many one-pipe radiators the vent just unscrews and a new one screws in when the system is off and cool. If it's seized, leaking or you're unsure, let a heating pro do it.

Why is only the top floor cold?

Usually it's system balance or main venting, which is a boiler-side job. In a rental, that's the landlord's to fix.

Is a cold radiator an emergency?

Usually not if the rest of the home is warm. A whole-home no-heat situation in winter is more urgent. Renters should tell the landlord and use 311.

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