What the heat distribution shows
- cold at top, warm at bottom — there's air in the system
- warm at top, cold at bottom — sediment or debris at the bottom
- the whole radiator cold, others warm — the shut-off valve or thermostatic valve is closed
- radiators lukewarm throughout the building — the issue is with the heat substation or its settings
What you can do yourself
If the radiator has a bleed valve, the air can be carefully released. Thermostatic heads are worth checking and moving, since they can seize up after standing unused for a long time.
But if the problem recurs every season or affects several flats, the cause is usually in the system itself, not in an individual radiator.
When flushing helps
If the radiators are cold at the bottom and heating capacity has declined over the years, sediment in the system is likely. The purpose of flushing is to restore circulation in the pipes and radiators.
One flat or the whole building
If only one radiator is cold, bleeding it, checking the thermostatic head, or cleaning that radiator is usually enough. If a whole flat or several flats are lukewarm, there's no point bleeding individual radiators — the issue is circulation, settings, or the heat substation.
In an apartment building it's worth comparing notes with neighbours before ordering work. This saves effort, since a fix applied to a single radiator won't change a building-level problem.
What we check in the system
- whether circulation is happening in all branches
- whether the thermostatic valves move or are seized
- whether the system pressure is at the usual level
- whether the heat substation's settings match the season
- whether the radiators are cold at the bottom, which points to sediment
Difference between a housing association and a private house
In an apartment building, a radiator's heat depends on the building's heat substation and the balance of the stacks. A single flat can stay lukewarm when the system is out of balance or a stack has become clogged with sediment — an in-flat job won't solve that.
In a house, the more common causes are system pressure, air in the circulation, pump operation and settings. There the whole system can be checked in one visit, since all the components belong to a single owner.
Frequently asked questions
- Am I allowed to bleed a radiator myself?
- If the radiator has a bleed valve and you have a cloth and a container at hand, the air can be released carefully. If water comes out under pressure right away or the valve won't close, it's best to leave the job to a technician.
- Why is a radiator warm at the top and cold at the bottom?
- This points to sediment at the bottom of the radiator or weak circulation. If it recurs in several radiators, it's usually sensible to look at the whole system rather than a single unit.