The short answer
If one radiator in your Northern Virginia home is cold at the top and warm at the bottom, it has air in it, and bleeding it takes two minutes. If the upstairs radiators are all cold, the boiler pressure is probably low. If every radiator in the house is cold, the problem is at the boiler: it isn’t firing, or the pump that moves the water has stopped.
All of that is about hot water systems, the kind with a pump and an expansion tank, heating radiators or baseboard. A steam boiler has a glass tube on the side with a water level in it. We don’t work on steam, and we’ll tell you so on the phone.
Which radiators are cold tells you the most
Swipe to see all columns →
Swipe to see all columns →
| What’s cold | Most likely | Who fixes it |
|---|---|---|
| One radiator, cold at the top | Air trapped in it | You, with a radiator key |
| The top floor, or the far end of a baseboard loop | Low pressure or air in the system | You can check the gauge. Refilling is ours. |
| One radiator, cold top to bottom | A closed or stuck valve on it | Try the valve, then call |
| Every radiator, boiler is running | The circulator pump or a zone valve | Call |
| Every radiator, boiler is silent | Thermostat, power, or the boiler isn’t lighting | Check the switch and thermostat, then call |
| Banging or gurgling, then cold spots | Air in the pipes | Bleed, then call if it comes back |
The $67 Heating Check
We check your furnace, heat pump or boiler before winter. Through December 31. See the offer
How to bleed a radiator
Turn the heat up so the boiler runs, then turn it off and let it sit for 15 minutes so the water settles and the radiators aren’t scalding. Find the small square valve at the top corner of the radiator. Hold a rag and a cup under it, and turn it a quarter turn counterclockwise with a radiator key (any hardware store has them for a couple of dollars). You’ll hear a hiss. When water comes out steady with no sputter, close it. Start on the lowest floor and work up.
Then look at the pressure gauge on the boiler. Cold, a two-story house usually sits around 12 to 15 psi. Bleeding lets out a little water, so the pressure can drop. Most systems refill on their own through a fill valve. If yours reads under 10 and stays there, or the radiators need bleeding every week, water is getting out or air is getting in somewhere, and that needs finding.
When it isn’t air
A circulator pump can seize after a summer of sitting still, especially on older systems. You’ll hear the boiler fire and feel the pipe right at the boiler get hot while the radiators stay cold. A zone valve can stick shut and leave one floor cold while the rest of the house is fine. And if the pressure gauge climbs past 25 to 30 psi when it runs, or the relief valve on the side is dripping, the expansion tank has likely lost its air charge. Turn the boiler off and call on that one.
Baseboard works the same way, just stretched out. A loop of copper pipe with fins runs along the wall, and the water cools as it goes, so the last room on the loop is always a little cooler than the first. If that last room is cold and the first is hot, the water is moving too slowly, which points back at air or the pump. Vacuum the fins too. Dust packed between them blocks the heat.
One more. If the boiler is short of water, sludge has built up inside, or it’s banging loud, those come from the inside of the system. Boiler repair covers the common fixes and boiler service before winter covers what a yearly visit catches.
What we check
On a cold-radiator call we read the pressure hot and cold, check the expansion tank charge, the circulator, the zone valves and the air vents, and look at the boiler’s burner and safeties. Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. If the boiler is near the end, what a new boiler costs gives the ranges, and our boilers page has the rest.
Book it
Book the heating check, call (703) 997-9757, or book online from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why is my radiator cold at the top?
Air is trapped in it. Air rises, so the top stays cold while hot water fills the bottom. Bleed it with a radiator key until water comes out steady.
Why are my upstairs radiators cold?
Usually low pressure in a hot water system, so the water doesn’t reach the top floor, or air collected there. Check the boiler gauge: cold, most two-story homes run about 12 to 15 psi.
Why are all my radiators cold but the boiler is on?
The water isn’t moving. The circulator pump or a zone valve is the usual cause, and it needs a technician.
Do you work on steam radiators?
No. SwiftPro services hot water boilers, radiators and baseboard. If your boiler has a sight glass with a water level, it’s steam, and we’ll tell you on the phone.
