If your radiator is warm at the bottom and cold at the top, there is air trapped inside it. Bleeding it takes about five minutes and you can do it yourself. If it is cold at the bottom and warm at the top, that is not air — bleeding will not fix it, and the system needs flushing.
This is the most common heating call we get in September and October, when people in Amsterdam turn the heating on for the first time since spring. Most of them do not need us. Here is how to tell which one you are.
Cold at the top or cold at the bottom?
Run the heating for ten minutes, then put your hand flat on the radiator, top and bottom.
- Cold top, warm bottom — trapped air. Air rises to the highest point of the radiator and pushes the hot water down. Bleed it.
- Cold bottom, warm top — sludge. Rust and magnetite settle at the base of the radiator and block the flow. Boiler manufacturers are clear that bleeding does nothing here; the system needs a professional flush.
- Completely cold while other radiators are fine — usually a stuck thermostatic valve. Pull the white knob off and press the metal pin underneath. If it does not spring back, the valve is seized.
- Every radiator cold — check the boiler pressure first. Below 1 bar most boilers stop circulating and go into fault.
How to bleed a radiator: the correct order
Most guides tell you to switch the heating off and start bleeding. That skips the step that makes it work.
- Open every radiator in the house fully and put the thermostat up. Let the system run for 10 to 15 minutes. This drives the air up to the bleed valves.
- Turn the thermostat right down and wait until the boiler stops and the water settles — around 10 to 20 minutes. Never bleed a hot system.
- Start on the ground floor , at the radiator furthest from the boiler. Air collects at the highest point, so you work upwards and finish with the highest radiator in the house.
- Close the valve of the radiator you are about to bleed. This is the step almost everyone skips, and it is the difference between actually removing the air and just letting water out.
- Open the bleed valve a quarter turn anticlockwise with a radiator key ( ontluchtingssleutel , a few euro at any Gamma or Praxis). Hold a cloth and a cup underneath. You will hear a hiss.
- Close it as soon as steady water appears — a clean dribble with no spitting. Then reopen the radiator valve and move to the next one.
- Check the boiler pressure at the end , once all radiators are done, and top up in one go if needed.
The pressure rule that is wrong for Amsterdam flats
Everyone tells you the gauge should read 1.5 to 2 bar. That is correct for a house with the boiler downstairs. If your CV ketel hangs in the attic or in a top-floor cupboard, it is not.
Pressure changes with height: roughly 0.1 bar for every metre. A boiler mounted at the highest point of the system sits where the pressure is lowest, so around 1 bar on that gauge is already enough to run the whole flat — Bosch says so in its own guidance. Chasing 2 bar on a top-floor boiler means the rest of the system is running higher than it needs to.
The same physics works against you when refilling. Mains pressure also drops about 1 bar per 10 metres of height, so four floors up there is not much left to fill with. If your pressure sits near 1 bar and will not climb, that is often the building, not a fault. Our guide to topping up a CV ketel walks through it.
One more thing for attic boilers: the most important bleed point is not a radiator at all, it is the automatic air vent on the boiler itself, plus any vent at the highest point of the pipework. If that vent is faulty, air keeps coming back no matter how many radiators you bleed.
When to stop and call a plumber
- Water comes out of the bleed valve but the radiator stays cold
- The radiator is cold at the bottom
- Banging or gurgling in the pipes while the heating runs
- Pressure keeps dropping every week after you top up
- The bleed valve is seized, or drips and will not seal again
- Air is back in the radiators a few weeks later
A sealed system should not keep taking in air. If it does, air is getting in somewhere, and repeatedly topping up adds fresh oxygenated water that corrodes the pipes faster. That is a diagnosis job.
Common questions
How often should I bleed my radiators?
Once a year is plenty for most homes, ideally at the start of the heating season in September or October. If you need to do it more often, something else is wrong.
Do I have to turn the heating off first?
Yes, but only after running it. Heat the system first so the air gathers at the vents, then switch off and let it cool. Bleeding a hot system sprays scalding water.
Why does only water come out, and the radiator is still cold?
Then there was no air to remove. Look at sludge, a seized valve, low pressure or a failing circulation pump instead.
Do I need a radiator key?
Usually. Some valves take a flathead screwdriver. A key costs a few euro at any DIY shop and is worth having in a Dutch flat.
Can I bleed radiators in a rented apartment?
Yes — bleeding is normal maintenance and does not involve opening anything sealed. Anything beyond that, including topping up a boiler you were never shown how to use, is worth reporting to your landlord first.
English-speaking plumber in Amsterdam
Your English Plumber covers Amsterdam, Amstelveen, Utrecht and Den Haag. Boiler and central heating work starts at €145 incl. VAT , we are usually on site within 2 hours , available 24/7, with a one-month warranty. No Dutch required, and you will understand every word of the invoice.
Call 06-24356980 or message us on WhatsApp .
