When the heating comes back on in autumn, radiators that sat idle all summer often need a little attention. Air trapped inside causes gurgling and a radiator that stays cold at the top. Bleeding it takes a few minutes with a key and a cloth, and this guide shows how to do it and when to leave the job to someone else.
Signs that a radiator has air in it
- Gurgling, bubbling or trickling noises when the heating is on
- Cold at the top, warm at the bottom
- One radiator stays cool even with the thermostat turned up, while the others heat normally
If a radiator is cold all over, the cause may be a stuck thermostatic valve rather than air. More on that below.
First: do you live in an apartment or a house?
In an apartment building, the heating is part of the building's shared systems, and the maintenance company (huoltoyhtiö) usually takes care of bleeding and balancing the radiators. Report the problem to them first. Some housing companies (taloyhtiö) prefer residents not to bleed radiators themselves, because air may have to be removed from the whole system and the pressure is controlled centrally. Ask before you reach for the key. If a radiator needs replacing, the housing company expects a renovation notice first.
In a detached house with a water-circulating heating system (vesikiertoinen lämmitys), for example with a boiler, district heating or a heat pump, you can bleed the radiators yourself or ask a plumber to do it.
What you need
- A radiator key (ilmausavain), sold in any hardware store. Some bleed valves open with a flat screwdriver instead.
- A cloth or small towel
- A small container, such as a cup
Step by step
- Turn the thermostat to maximum so the radiator valve is fully open.
- Check your heating system's instructions. Some systems advise stopping the circulation pump for a while before bleeding, so the air can rise to the top of the radiators. Follow what the instructions for your boiler, heat pump or district heating unit say.
- Find the bleed valve. It is a small square-headed screw at the top corner of the radiator, usually at the opposite end from the thermostat.
- Hold the cloth and the container under the valve, fit the key and turn it slowly anticlockwise, about a quarter of a turn.
- Let the air out. You will hear a hiss. When water starts to come out steadily without spitting, close the valve by turning the key clockwise. Don't overtighten it.
- Repeat on the other radiators that show signs of air.
- Restart the circulation pump if you stopped it.
Be careful: the water in the radiator can be hot, and it can mark the floor and the wall, so keep the cloth ready.
Check the pressure afterwards
This step applies to houses with their own water-circulating system. Bleeding releases some water from the system, so the pressure drops slightly. Check the pressure gauge (painemittari) on the boiler or the heat distribution unit. If it is below the value recommended for your system, top up the water according to the system's instructions.
Don't guess the right pressure. Both too low and too high a pressure can cause problems, and the correct value depends on the system. If the pressure keeps dropping after topping up, there may be a leak, and the system should be checked.
Thermostatic valves can stick after summer
A thermostatic valve has a small pin that moves in and out to control the flow of hot water. After a summer with the heating off, the pin can stick in the closed position, and the radiator stays cold even though it has no air in it.
Turn the thermostat between minimum and maximum a few times. This often frees the pin. If the radiator still doesn't warm up, the valve may be worn or faulty. In an apartment building, report it to the maintenance company. In a house, a plumber can check the valve and replace it if needed.
Uneven heat between rooms: balancing
If some rooms are warm and others cold even though there is no air in the radiators, the system may need balancing (perussäätö, also called tasapainotus). Balancing means adjusting the valve pre-settings so that hot water is distributed evenly across the radiators.
In an apartment building, balancing is done for the whole building and organised by the housing company. In a detached house, a plumber can balance the system, which is also a good moment to check the condition of the valves.
When to call a plumber
Bleeding is a simple job, but some problems need a professional:
- Air keeps coming back soon after bleeding.
- A bleed valve, a radiator valve or a pipe joint is leaking.
- Thermostatic valves are worn, broken or no longer respond.
- A radiator stays cold after bleeding and after checking the thermostat.
- The pressure in a house's heating system keeps dropping.
- The radiators or the pipework are old and failing, and renewal is worth considering.
In a detached house, the labour for larger heating work can qualify for the household tax credit.
Summary
- Gurgling and a cold top usually mean air in the radiator.
- In an apartment building, contact the maintenance company first.
- Open the bleed valve slowly, let the air out and close it when water appears.
- In a house, check the pressure afterwards and top up according to your system's instructions.
- Turn stuck thermostats between minimum and maximum, and consider balancing if the heat is uneven.
If your radiators need more than bleeding, see our radiator installation page, which also covers thermostatic valves, bleeding and balancing, or radiator pipework renewal for older systems. A leaking joint can be fixed as one of our small plumbing jobs. Contact us to book a visit.