Radiator stays cold or only warms up halfway: what it means

Cold at the top, warm at the bottom: that is air

Run your hand up the face of the radiator. If the bottom half is properly hot and the top stays stubbornly cool, air has collected in the highest point of the radiator body and is stopping hot water filling that section. This is the most common radiator complaint in flats and by far the easiest to fix.

Air gets in when the system is refilled after work on the building's heating, after a valve has been changed, or sometimes just gradually over a heating season as small amounts of dissolved air come out of the water. It is not a sign anything is wrong with the radiator itself.

How to bleed a radiator properly

Every panel radiator has a small bleed valve, usually a square-socket screw at one top corner. Turn off the room thermostat or set the valve to its lowest setting first if you can, then have a cloth and a small container ready, because water will follow the air.

Fit the bleed key onto the valve and turn it slowly, a quarter turn at a time. You will hear a hiss as air escapes. Keep the key in place until the hiss stops and a steady trickle of water comes out, then close the valve firmly but without forcing it. Wipe up any drips straightaway, since radiator water can mark flooring.

If the radiator warms evenly afterwards, that was the whole problem. If it stays cold at the top even after bleeding, or the valve will not turn, or the top of the radiator is still cool the next day, something else is going on and it is worth having it looked at rather than repeating the bleed.

• Turn the bleed key a quarter turn at a time, not all at once
• Keep a cloth and container underneath before you start
• Stop as soon as water runs steadily and close the valve
• Check the radiator again after an hour once it has had time to fill
• If it will not bleed or refills with air within days, stop and call a plumber

Cold at the bottom, warm at the top: suspect sediment

The opposite pattern is more of a concern. If the top of the radiator heats up fine but the bottom third or so stays cold, air is not the issue, because air rises and settles at the top, not the bottom. What is sitting there instead is usually sludge: rust and mineral sediment that has settled out of the system water over the years.

Bleeding will not shift this, since there is no air to release. The sediment sits in the lower part of the radiator body and blocks water flow through that section. Older radiators, and radiators that have never been flushed, are the ones most likely to show this pattern.

When it is a building-wide problem, not just your radiator

If several flats in the stairwell mention the same thing around the same time, or radiators in different rooms of your own flat are all underperforming at once, the cause is more likely in the building's heating system than in one radiator. Uneven pressure, a valve issue in the substation, or work recently done elsewhere in the building can all show up this way.

This is worth raising with the korteriühistu board or property manager rather than treating flat by flat, since a shared cause needs a shared fix, often a proper flush or balancing of the whole system by a heating specialist. One resident bleeding radiators repeatedly without result is usually a sign the problem sits upstream.

When to call a plumber instead of trying more yourself

Sediment does not come out through the bleed valve, so a radiator that is cold at the bottom usually needs to be flushed out, or in older cases replaced. This is plumbing work, priced from 45 € an hour, and it is worth doing properly rather than living with a radiator running at half capacity through winter.

A valve that will not turn, a bleed key that strips the screw, or a radiator that leaks once bled are also jobs for a plumber rather than more force. If the radiator itself is old, corroded, or simply undersized for the room, radiator installation starts from 85 € per job and is often more sensible than repeatedly nursing a tired unit through another heating season. For anything simpler, such as fitting a new bleed valve or a decorative cover, that falls under odd jobs from 39 € an hour.