Knowing how to bleed radiators is one of the most useful bits of heating know-how at the start of winter: if a radiator is cold at the top and warm at the bottom, air has probably collected inside. This guide is for households in Antalya, Turkey with radiators that aren't heating properly and who want to bleed them themselves. Drawing on Vaillant's user manuals, it covers the tools you need, a step-by-step bleeding method, why you must check boiler pressure afterwards and why some radiators still won't heat up after bleeding.
Why Does Air Build Up in Radiators?
A combi boiler heating system is a sealed circuit: water circulates continuously between the boiler, the pipes and the radiators. Air can get into the circuit when the system is topped up, when a component is replaced, or after the system has been off for a long time. Because air is lighter than water, it gathers at the top of the radiators and stops hot water filling the whole panel. The result is radiators with cold tops and a boiler that has to run for longer.
Signs of Air in Your Radiators
- The top of the radiator is cold or lukewarm while the bottom is hot
- Gurgling, trickling or running-water noises from radiators or pipes
- Some radiators on the same system heating noticeably less than others
- The pressure indicator flashing on the boiler display (according to the ecoTEC pure manual, it flashes when pressure is outside the permitted range or a venting routine is running)
What You'll Need
- A radiator bleed key: as the Vaillant ecoTEC intro user manual notes, a bleed key can be used to release the air. Some valves open with a flat-head screwdriver instead.
- A cloth and a small container: to catch the water that comes out with the air.
- Access to the boiler's pressure gauge: to check pressure afterwards and top up if needed.
How to Bleed Radiators: Step by Step
- Turn the heating off and let the radiators cool. This reduces the risk of scalding, and with the pump stopped the air settles at the top of the radiators.
- Open the radiator valves. Vaillant's manuals ask for all radiator (thermostatic) valves to be open when the heating system is being filled.
- Find the bleed valve. According to the ecoTEC intro manual, air is released from the designated point on the radiator, the small valve at the top left or top right corner.
- Hold the cloth and container under the valve and fit the key.
- Open the valve slowly and only slightly. You'll hear a hiss as the air escapes. Don't unscrew the valve completely.
- Close the valve as soon as water appears. A steady flow of water means the air in that radiator is gone.
- Repeat on the other radiators. Bleed every radiator that isn't heating properly.
- Check the boiler pressure. Top up if needed, then switch the heating back on.
The ecoTEC intro manual recommends repeating the filling and bleeding steps if necessary. Once the heating has been running for a while, feel the radiators again; if the top is still cold, you can bleed it once more.
Mind the Model Differences
Vaillant's manuals aren't uniform on this. The ecoTEC plus and intro manuals describe bleeding as something the user can do, while the troubleshooting tables in the ecoTEC pro and pure manuals recommend having air in the heating system removed by an authorized dealer. Bleeding radiators is generally safe to do yourself, but venting air from inside the boiler itself, or a persistent air problem, is a job for a technician.
Common Mistakes When Bleeding Radiators
- Unscrewing the valve completely: the bleed valve only needs to be opened a little. A valve that comes right out is hard to refit against pressurized water and can flood the floor.
- Bleeding while the system is hot: hot water and steam can scald, and with the pump running the air keeps circulating inside the radiator.
- Forgetting to check pressure: bleeding several radiators can drop pressure noticeably, and the boiler may stop after a while because of low pressure.
- Overtightening the valve: forcing it shut can damage the valve seat and seal; stop as soon as the water stops.
- Treating every problem with bleeding: needing to bleed again and again can be a sign of a leak or an installation problem.
Check Boiler Pressure After Bleeding
Some water escapes along with the air, so system pressure falls. That's why Vaillant's manuals put a pressure check, and a top-up if needed, straight after the bleeding step. For example, the ecoTEC pro manual says pressure should be between 1.0 and 2.0 bar on a cold system. We explain the right pressure and how to top up in detail in what should boiler pressure be.
Radiator Still Not Heating After Bleeding?
Not every heating problem is caused by air. If a radiator still won't heat up after bleeding, check these possibilities:
- Radiator valve closed or thermostatic head stuck: the pin on a thermostatic valve can stick after a long period closed.
- Low boiler pressure: without enough pressure, water may not reach radiators on upper floors or at the far end of the system.
- Bottom of the radiator is cold: a radiator that is warm at the top and cold at the bottom usually has sludge and sediment inside, not air. The fix is radiator cleaning, not bleeding; we explain the difference in our radiator cleaning guide.
- All radiators are cold: if the boiler isn't heating, the problem lies with the boiler settings, the room thermostat or the pump, not the radiators.
- Radiator too small for the room: if the radiator heats up but the room doesn't, it may be undersized; our radiator size calculator gives a rough idea of what your room needs.
How Often Should Radiators Be Bled?
There's no fixed schedule; bleed them when the symptoms appear. Even so, it's good practice to check your radiators at the start of the heating season, after topping up the system and after any work on the pipework. If you need to bleed very often, air or fresh water is probably getting into the system continuously, which points to a leak or an installation problem.
Notes for Antalya
Antalya's heating season is short, so radiators stay cold for most of the year, and cold tops on the first run of the season are a common sight. Running the boiler before the first cold day, checking the radiators, bleeding them and topping up the pressure improves both comfort and boiler efficiency. For persistent air, constant pressure loss or suspected sludge, Devka Doğalgaz's radiator heating installation and boiler maintenance services can help.
Safety Warning
Bleeding radiators involves only the water circuit; it never requires touching the gas line or the inside of the boiler. If you smell gas around the boiler, close the gas valve without touching any electrical switches, open the windows, leave the building and call Enerya Antalya's 187 natural gas emergency line from outside.
If your radiators have a persistent heating problem, call Devka Doğalgaz on +90 553 028 82 80. You can book an on-site check anywhere in Antalya through our contact page.
Frequently asked questions
How do I know my radiators need bleeding?
The classic sign is a radiator that is cold at the top and warm at the bottom. Gurgling, trickling or bubbling noises from radiators or pipes can also mean there is air in the system.
Should the boiler be on when I bleed radiators?
It is safer to turn the heating off and let the radiators cool: you reduce the risk of scalding, and once the pump stops the air collects at the top of the radiator. Vaillant's manuals also describe bleeding as one step in refilling the heating system.
What can I use if I don't have a bleed key?
Some radiator bleed valves are made to open with a flat-head screwdriver. For square-headed valves, an inexpensive radiator key from a hardware shop is far better than forcing the valve and damaging it.
The radiator still won't heat up after bleeding. What now?
First check that the radiator valve is open and that boiler pressure is high enough. If the bottom of the radiator is cold and the top is warm, the problem is usually sludge rather than air, and the radiator may need cleaning.
Why did boiler pressure drop after bleeding the radiators?
Some water escapes along with the air, so pressure falls. Check the gauge when you finish; if it is below the range in your manual, top up using the boiler's filling valve.
