Radiator not getting warm – what to do?
Difficulty: Easy · Time: approx. 10 minutes
The heating is running, but one radiator stays cold or only gets warm at the bottom – and there's a faint gurgling in the pipes? Then there's very likely air trapped in the radiator. It collects at the top and pushes the hot water out of the way.
Bleeding a radiator is the easiest heating fix there is: all you need is a small square-socket key and a cup. Ten minutes and the air is out – afterwards it's worth taking a quick look at the system's water pressure.
What you'll need
- Radiator bleed key (small square key from the hardware store)
- Cup or mug to catch the water
- Cloth or old towel
- A flat-head screwdriver works on some valves too
- Optional: hose for topping up (only in your own house)
Step by step
- 1
Turn the thermostat all the way up
Open the thermostatic valve on the affected radiator fully. If you have access to the heating system, switch off the circulation pump briefly – or wait 30 to 60 minutes instead. This lets the air collect at the top of the radiator instead of being churned through the pipes.
- 2
Find the bleed valve
The bleed valve sits at the top of the radiator, on the side opposite the thermostat – a small valve with a square socket. Put the cloth underneath and hold the cup at an angle below it, because air will come out first, then water.
- 3
Open the valve slowly
Fit the bleed key and slowly turn the valve a quarter to half a turn anticlockwise – never unscrew it completely. You'll hear a clear hissing: that's the air escaping.
- 4
Close it once the water runs bubble-free
At first the valve usually sputters out a mix of air and water, then a steady stream without bubbles follows – now turn the valve clockwise again, hand-tight is enough. Careful: the water can be hot.
- 5
Check the system pressure
Bleeding lowers the pressure in the heating system slightly. So take a look at the pressure gauge on the boiler: in a single-family house, 1.5 to 2 bar is typically fine. If the needle sits below that, top up water with a hose via the boiler's small fill-and-drain valve. In a rented flat, report the low pressure to your landlord or property management instead.
- 6
Set everything back and test
Switch the circulation pump back on and set the thermostat to its usual level. After a short while the radiator should heat up evenly – without any gurgling noises.
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Upload a photo →Frequently asked questions
- How often should I bleed my radiators?
- Once a year at the start of the heating season is a good rhythm – plus whenever a radiator gurgles or stays cold at the top. Air tends to build up especially after water has been topped up or work has been done on the system.
- Warm at the bottom, cold at the top – what does that mean?
- That's the classic sign of trapped air: it rises to the top and pushes the heating water out of the way, so the upper part stays cold. After bleeding, the radiator should heat through evenly again.
- Do I have to top up water after bleeding?
- Some water always escapes along with the air, so the system pressure drops slightly. Check the pressure gauge: 1.5 to 2 bar is typical for a single-family house. If the pressure is below that, top it up – as a tenant, inform your landlord or property management instead.