Radiator cold at the top? Here’s why
A radiator that’s warm at the bottom and cold at the top has air trapped in it. Hot water can’t reach the space the air is holding. Bleeding the radiator lets the air out and the water fills the whole thing again.
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From one of our jobs
A cast iron radiator on a hot water boiler
Right now: Open the small bleed valve at the top of the cold radiator with a key and a rag until water comes out, then close it.
Air gets into hot water heating systems through new fill water and small leaks, and it rises to the top of the highest radiators. Most radiators have a small bleed valve near the top. Open it a little with a radiator key, let it hiss until water comes out, then close it.
If the whole radiator stays cold, it’s not air. It can be a closed valve, a circulator pump that isn’t moving water, or low pressure at the boiler. If you bleed radiators every few weeks, the system is pulling in air somewhere and needs a look.
Quick answers
What people ask about cold radiators
Why is my radiator cold at the top and hot at the bottom?
Air is trapped in the top. Bleed it at the small valve near the top until water comes out.
Why is my radiator completely cold?
Check that its valve is open. If it is, the boiler pressure may be low or the circulator pump may not be moving water to that zone.
Why do my radiators bang or knock?
Usually air or pressure swings in the system. On steam heat it’s water sitting in the pipes.
How do I bleed a radiator?
With the heat off, hold a rag under the bleed valve, open it a quarter turn with a radiator key, and close it when water comes out steady. Check the boiler’s pressure after.
Who do I call about radiators and boilers in Northern Virginia?
Call SwiftPro at (703) 997-9757. We service and repair hot water boilers and radiators across Northern Virginia.
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SwiftPro Heating, Cooling & Plumbing
4230 Lafayette Center Dr N, Chantilly, VA 20151
44679 Endicott Dr, Suite 211, Ashburn, VA 20147
SwiftPro Plumber & Water Heaters
4200 Lafayette Center Dr, Suite N, Chantilly, VA 20151
Virginia Class A contractor license #2705192276