Why is there no pressure when I bleed my radiator?

Author: Edgardo Wuckert DVM  |  Last update: Friday, October 3, 2025

If you have recently bled your radiators, the pressure will drop slightly because you've released the trapped air in the system. This air needs to be replaced with water to get the pressure back up again.

Why have I lost pressure when I bleed my radiator?

One of the most common causes of pressure loss is if you've recently bled your radiators. As air is released from your central heating system, it lowers the pressure. So make sure you check the pressure gauge after bleeding a radiator.

Why is there no air coming out when I bleed my radiator?

If no water or air comes out when you bleed the radiator, then the valve could be blocked with paint. Close the inlet and outlet valve at each end of the radiator, then remove the screw from the centre of the bleed valve.

Why is nothing happening when I bleed my radiator?

Make sure you've properly bled the entire radiator. If it's still not working, there might be a larger issue with the system, such as a faulty valve, pump, or circulation problem. It's also possible that the thermostat isn't functioning correctly.

How to increase pressure after bleeding radiators?

Bleeding radiators, need to adjust water pressure It should be just where water from your water supply is fed into the heating system. Raise the pressure by turning the screw on top of the valve clockwise. Watch the pressure gauge and go to about 12psi, and then a few more psi if really needed.

How to Bleed Radiators 'Properly'

How do you bleed a radiator without losing pressure?

Bleeding your radiator in 6 steps
  1. Turn your heating off and allow time for it to cool down.
  2. Take a towel and a jug and place both underneath the bleed valve on the radiator.
  3. Insert the bleed key and turn it slowly, anti-clockwise.
  4. Air will escape and you will hear a hissing noise. ...
  5. Repeat on all the radiators in your home.

How to increase pressure in radiator system?

If below 1 bar, your boiler has a low water pressure and needs re-pressurising. Locate the filling loop, often found on the underside of your boiler. Open both valves to allow water into your heating system. Keep an eye on the pressure gauge and close the valves when the pressure reaches 1.5 bar.

What happens if you bleed too much water out of a radiator?

If a large volume of water has poured out, it's possible that you opened the valve fully. We recommend not opening it all the way. If too much water escapes your radiator, it will be replaced with fresh water, which can bring air with it, and can send your radiator back to square one after your bleeding attempt.

How can I tell if my radiator is clogged?

The Symptoms of a Clogged Radiator can be anything from the temperature gauge showing higher temps to steam billowing from under the hood of your vehicle.

How to unblock a radiator bleed valve?

Place a bucket or bowl under the TRV at the bottom of your radiator and loosen the TRV at the nut joint with a spanner. Open the bleed valve using the bleed key to remove any air in the system. Sludge and dirty water will begin to drain out. Then, loosen the lockshield valve and repeat.

Should you bleed radiators with the pump on or off?

Aside from the danger of working with a radiator that has the heating on, it's also an inefficient bleeding process. If the pump is running when you let out air, this will actually cause the system to draw in more air from elsewhere.

How do I know if my air is trapped in my radiator?

Even a small amount can create air pockets which prevents proper circulation of coolant. Signs and symptoms of radiator airlock include: Overheating during normal driving. Heater not functioning correctly.

How long should air come out of radiator when bleeding?

Usually, it will take between 20 and 30 seconds to effectively bleed a radiator, but it might take up to a full minute in the case of larger radiators.

How much water should come out when bleeding a radiator?

You'll likely notice some drips emerging when initially turning the bleed screw in an anti-clockwise direction. And water would pour out once the air was released, if the valve was to be opened fully. However, completely opening the valve should be avoided.

What happens when radiator loses pressure?

If the cap cannot maintain the correct pressure, the coolant might boil off, reducing its ability to absorb heat, and this increases the temperature of the engine, leading to overheating and engine failure. This can be particularly noticeable during long drives or in stop-and-go traffic.

Why is there no water flowing through my radiator?

This is an indication that you have debris, a blockage, or most likely, sludge, which has accumulated in the radiator. Hot water is not able to circulate because of the build-up at the bottom of the radiator. The most efficient and safest way to deal with this problem is to seek professional help.

How to unblock a radiator core?

Remove the radiator fill cap and pour the heavy-duty radiator flush into the radiator. Fill the remaining empty part of the radiator with fresh water. Place the cap back on the radiator. Start your vehicle and keep it running for almost 15 minutes, allowing the radiator flush to move through the entire cooling system.

How to tell if a radiator is circulating?

Take off the pressure cap. Start the engine and watch the coolant to see if it begins circulating.

How to burp a coolant system?

Burping (so named because of the noise made by the bubbles of coolant exiting the radiator filler neck) is done with the radiator cap removed on cars without a valve. You wait for the car to warm up so the thermostat opens, and then the pressure of the expanding coolant being heated drives the air out.

Why is no water coming out of my radiator when I bleed it?

It's advisable to check first whether it's a stuck pin, as these sometimes get stuck in an 'off' position, which needs a quick wiggle to release the pin and allow the water to flow. However, valves can break down, and older radiators may well have degraded thermostatic valves, especially if they're used often.

What if bleeding a radiator doesn't work?

If your home radiators fail to heat up after bleeding, you should first check for issues with your thermostatic radiator valves, such as a stuck pin on the valve. Alternatively, you can perform a radiator power flush or take steps to ensure your heating system is correctly balanced.

Do you bleed a radiator until it stops hissing?

In this case, place the blade of your flathead screwdriver in the groove. Then rotate slowly anti-clockwise a quarter until you hear air hissing out. Never fully release a bleed valve. Pressure in the system will force excess water out all over your floors.

Why is my radiator not building pressure?

Bad Water Pump or Thermostat

If the thermostat goes down, the system will not know when to release fluid into the radiator, and if the water pump fails, the system will not have the pressure necessary to circulate the coolant. If either of these things happens, the radiator will not work as designed.

Will bleeding radiator reduce pressure?

Yes. During the process of bleeding radiators, air is released from within them, which in turn reduces the pressure in your boiler system.

What to do after bleeding the radiator?

So, let's discuss the steps you must complete to ensure your radiators get hot after bleeding.
  1. Step 1: Check Whether Your Heating System is Balanced or Not. ...
  2. Step 2: Check Your Thermostatic Radiator Valve For a Stuck Pin. ...
  3. Step 3: Powerflush Your Heating System to Remove Blockages.

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