Vacuum Breaker

The vacuum breaker, what it looks like, what it does, how to undo for cleaning


It is a simple device, it seals the boiler when it's up to pressure (a little rubber gasket on a metal pin is forced upwards by steam pressure and creates a seal), when the boiler cools and the steam pressure drops, it breaks that seal. This prevents a vacuum (just low pressure actually), forming in the boiler after cooling. Preventing a few problems such as old milk or other rubbish being sucked back through the milk wand, if you open the valve on a cold machine. It also seems to prevent false warm ups, ensuring that the boiler really is up to pressure and the boiler pressure does not drop to 0 as soon as you open the steam wand first thing after warm up.

A faint hiss coming from the top of your boiler all the time…check this out. The vacuum breaker for an Izzo Vivi is shown and you can actually split these and clean/descale the parts inside. These are quite common, although there are some makes that apparently don't split for cleaning (to be honest I am not sure how they could be manufactured, but apparently they exist)??

The updated vacuum breaker (shown below) used on the Alex MKII (the Vivi MKII one is almost identical and I will soon be getting one of each to compare and identify the exact differences). This is also the style of breaker used on many other machines such as the Quickmill Andreja Premium.


On inspection it appears that this is a direct replacement for the old valve and can be fitted on all machines using the valve in the picture above. I took one apart to have a closer look and as you can see, it’s a very simple device. Pressure in the boiler pushes the brass pin with the silicon (or Viton) O ring onto the nylon seating and seals the boiler as it comes up to steam. It has advantages over the old style valve of having a larger sealing area and a slightly heavier pin, which should encourage a more positive closure. However the valve mounts directly onto the boiler and the sealing surfaces will be closer the boiling waters surface. This may cause more deposits on the seating surface (which could eventually affect the seal) and more spitting of water out of the valve just before it closes. If I were updating the one on my machine (Alex not a MKII), I would be inclined to try and fit it onto the end of a 1 or 2 cm brass extension fitting. Also it needs to be removed to disassemble for cleaning, although often a long press when the machine is under pressure will vent steam and "steam clean" the sealing surfaces of any deposits.


An extract from our forum below

if you end up with a 'tainted' boiler it means that water/milk has been sucked into the boiler and the only solution (as I understand it) is a lot of cleaning out/flushing/descaling….at the worst a full strip down to clean burnt milk particles off the heating element!

The above is quite true and I was given to understand, can happen on commercial machines with more than one steam/hot water want under heavy/simultaneous use conditions. My reply to any concerns you may have with a single group prosumer home machine is:

A tainted boiler is a bit of a bugger, but it would be unlikely on any machine with a Vac breaker. The combination of events on a machine equipped with a vac breaker would have to be as follows and is extremely unlikely, in fact I doubt it could ever happen, even under the conditions described below..

The vacuum breaker sticks with enough force, that sufficient vacuum can be maintained in boiler, after the machine has been switched off, to suck milk (or milky water), up through a steam valve that was almost totally closed. The steam pipe having been immersed and left in a solution of milk or milk and water when the machine is switched off

  • It would be unlikely knowing the construction of the breaker valves that one could stick with enough force
  • I say steam valve almost totally closed as it would be obvious if it wasn't, especially as it will be submerged
  • You can't get milk sucked into a prosumer 1 group machine with a vacuum breaker if there is any steam pressure in the boiler.

So if you have a Vacuum Breaker valve on your machine, I don't believe you have anything to worry about.