When radiators are turned on but staying cold or only warming at the bottom, something is interfering with heat circulation. This often shows up at the start of colder weather or after a system has been off for a while. Whether you own a home or manage a building with radiator heat, the underlying causes and solutions are usually the same.
In one recent situation, a property manager in Tysons, VA reported that multiple radiators were not producing heat and was told trapped air was likely the issue, but the radiator controls were damaged and difficult to identify. That combination is common and can make troubleshooting confusing.
Radiators depend on hot water or steam moving freely through the system. When circulation is disrupted, heat output drops or stops entirely.
- Air trapped inside the radiator
- Closed, stuck, or damaged radiator valves
- System imbalance sending heat to some radiators but not others
- Low boiler pressure in hot water systems
- Sediment or sludge buildup inside older piping
Air trapped in the system is one of the most frequent causes, which is why bleeding radiators is often the first recommendation.
Bleeding a radiator means releasing trapped air so hot water can fill the radiator completely.
Air naturally enters radiator systems over time. It can be introduced when the system is refilled, after maintenance, or when the heat is turned off for extended periods. Once inside, air rises to the top of the radiator and blocks proper circulation.
Radiators that need bleeding often show clear symptoms.
- Warm at the bottom but cold at the top
- No heat at all while other radiators work
- Hissing or bubbling sounds
- Problems that appear after the system was recently turned back on
These symptoms strongly suggest trapped air, but they do not rule out valve or hardware issues.
Most radiators have a bleed valve near the top on one side.
It may look like:
- A small square valve requiring a radiator key
- A slotted screw
- A small recessed valve built into the radiator
In older homes and multi-unit buildings, the valve may be painted over, difficult to access, or missing a usable turning head.
Yes. A damaged or missing radiator control can stop heat entirely.
- The internal valve may be stuck closed
- The valve stem may be damaged
- The radiator cannot respond properly to system pressure
In these cases, bleeding alone will not fix the problem. The valve itself needs to be inspected to confirm it can open and allow flow.
Radiator systems are durable, but age and shared piping can introduce complications.
Older systems may have:
- Worn valves that no longer regulate flow properly
- Uneven distribution across multiple floors or zones
- Higher likelihood of air pockets forming after seasonal startup
In buildings with multiple radiators on the same loop, one issue can sometimes affect several units at once.
Bleeding can be a DIY task when:
- The bleed valve is intact and accessible
- The radiator valve appears functional
- System pressure remains stable afterward
Professional service is recommended when:
- The bleed valve or control knob is broken
- Bleeding does not restore heat
- Multiple radiators are affected
- The system loses pressure after bleeding
We often find that bleeding uncovers deeper issues that require adjustment or repair to restore consistent heat.
If bleeding does not resolve the issue, the next step is a system-level inspection. This may include checking radiator valves, verifying boiler pressure, and identifying circulation or balance problems within the system.
Catching these issues early helps prevent ongoing heat loss and unnecessary wear on the equipment.
B.L. James & Son has been helping homeowners and property managers in Tysons, VA & surrounding areas keep boiler and radiator systems running reliably for over 25 years. If your radiators are not heating properly or you suspect trapped air or damaged controls, we can help identify the cause and recommend the right fix. Contact us today to schedule a heating system inspection and restore reliable heat to your home or building.
The B.L. James & Son team likes to move quick and reply to customer inquiries the same business day. Once we troubleshoot the issue, estimates are provided the same day or by the end of the next day. Our work begins the moment you call, and since we’re open 24 hours a day there’s no reason to wait. Call B.L. James & Son anytime, we’ll be there to help.
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B.L. James & Son Is a veteran-owned mechanical contractor providing plumbing, heating and cooling services to residents and business in Arlington, Virginia and the surrounding community.
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