How to Repressurize a Boiler

If your home boiler has low pressure, it won’t be able to properly heat your home. Thankfully, there are several ways you can repressurize a boiler yourself without calling a professional. Depending on the age and type of boiler, you may be able to repressurise it yourself by using the filling key to add water or by opening the water filling valves. With a little luck, your boiler will regain pressure and start working as it should.

Method 1 - Repressurizing Using a Filling Key

 1.  Turn off the power to the heating system. After turning your boiler off, wait a few hours so it can cool. If you don’t turn it off and allow it to cool before working on it, you could damage the system or hurt yourself. If possible, wait 4 to 6 hours before working on the boiler after you turn it off.

2.  Reach under the boiler and pull out the tray that is concealed underneath. On newer boilers, the tray may be plastic. Older boilers may have metal trays. Whatever the tray is made of, gently pull it out of the boiler.

3. Remove the filling key from the tray. When you remove the tray from the boiler, you’ll notice a small key-shaped piece of plastic or metal attached to it. The key will probably be secured to the tray by a clip of some sort. Gently pull the key out of the clip.
4.   Place the filling key into the key manifold keyhole. The key manifold keyhole is located right next to the manifold nut. This is a square nut that you’ll need to turn later. Depending on the age and make of your boiler, the key manifold hole and nut may be made from metal or plastic. Once you locate the key manifold, gently slide the filling key into it.
  • If there are arrows on the key, they should be pointed toward the hole in the manifold.
  • The key should fit snugly into the manifold

5.  Turn the key to the unlocked position. Look for a padlock, lock, or another symbol that represents the closed position on the manifold. Then, turn the key so it is in the unlocked position. This will be symbolized by an unlocked padlock. To unlock the manifold, you’ll have to turn the key approximately 45 degrees.
  • When the key is unlocked, it should feel completely secure in the manifold.

6.  Use a wrench to rotate the manifold nut counterclockwise. Turn the nut (located next to the manifold keyhole) slowly and gently. Once you turn it about halfway around, you should hear water moving into the boiler system. The pressure on the system should begin to rise.

7.  Look at the boiler’s pressure gauge and turn the nut when the gauge hits 1.5 bars. As the water fills the boiler, you should see the arm on the pressure gauge slowly moving up. The gauge on many systems will read between 0 and 4 bars. When you see the arm reach 1.5 bars, turn the manifold nut clockwise until the water stops. Then, continue to watch the pressure gauge until the pressure has equalized at 1.5 bars.

8.  Turn the release knob on your nearest radiator, if there is too much pressure. If you see the arm on the pressure gauge go into the red, you'll need to release pressure from the system. Using a wrench or protective mitts, turn the release knob (next to the release valve) on the radiator. Make sure you’re standing clear of the release valve, though, as it will release hot pressurized air. This should lower the pressure on your boiler within seconds.

9.  Turn the key to the locked position. After you’ve turned the nut back to the off position, gently turn the manifold key back into the locked position. By doing this, you’ll make sure that no one can accidentally turn the manifold nut (and increase the amount of water in the boiler).

10.  Remove the filling key and return it to the tray. Gently remove the key from the manifold. When you do this, you may see a few drops of water drip down. This is normal. After removing the key, gently place it back into the tray. Then, slide the tray back into the slot beneath the boiler.
  • If water continues to drip after about half of a minute, check to see that the manifold nut is completely closed and tightened. If it is not, water will continue to enter the boiler and drip down.
  • If the key gets stuck when trying to remove it, contact us. You could damage the boiler or cause the unit to become over pressurized by taking it out incorrectly.

11.  Turn the boiler back on. Once you’ve returned the key to the tray and replaced the tray, you’ll need to hit the main power switch and power the boiler back on. At first, you’ll notice the pressure fluctuate just a little bit. However, it should stabilize within a few minutes.
  • If your boiler begins to depressurize again, you’ll need to let us know so we can arrange for a certified boiler repairman to inspect and repair it.

Method 1 - Adding Water and Raising Pressure through Filling Hoses

1.  Switch your boiler off. Hit the main power switch and power down your boiler. Wait 4 to 6 hours for the system to cool down completely. If you have the time, allow your boiler to cool off even longer. You don’t want to work on your boiler if it is hot.

2.  Check to see the that filling loop hoses are properly attached. Turn the hoses to see that they’re attached properly (and tight). If they’re loose, water may be leaking out of the hoses instead of going into the boiler. This can cause your boiler to lose pressure.
  • If they’re loose, tighten them. In some cases, you may need a wrench to tighten them completely.
  • Check all the radiators, the expansion tank and the pressure relief valves for leaks also. Even a small leak can lead to a drop in pressure over enough time.
  • If hard water and scale buildup inside pipes is potentially a problem in your area, this could also cause pressure fluctuations if a pipe is partially blocked. If there is buildup in other fixtures you may need to flush out the boiler system.

3.  Use a screwdriver to open the filling valves. The filling valves are located next to where the hoses connect to the boiler. Turn your screwdriver counterclockwise to open the valves. This will allow cold water to enter the boiler. As you do this, you should begin to hear water flowing.
  • If valves are difficult to turn, spray with WD 40 and wait for a few minutes. Trying to force the valve to turn can damage it or strip the screw head.

4.  Close the filling valves when the pressure gauge hits 1 bar. As cold water enters the boiler, the arm on the pressure gauge should begin to move up from 0. When it moves to 1 bar, turn the valves clockwise into the off position. This will turn off the flow of water. After 30 seconds, the pressure in the boiler should stabilize.
  • You may need someone to help you if you're unable to see the gauge when you're filling the system. Stop filling immediately if you hear the pressure valve releasing water.

5.  Turn the boiler back on. After the pressure has stabilized at 1 or 1.5 bars you should hit the main power switch to power the boiler back on. At this point, your boiler should be pressurized and run properly.
  • If your boiler starts to lose pressure again, turn it off and contact us so we can arrange for a certified boiler repair person to attend.

If you are still experiencing issues please email