PortafilterProcrastinator My question on the VB stems from the amount of pressure required to close it. If opening the steam wand leads to a drop in pressure in the SB (which I am assuming it must) then can this theoretically lead to the VB opening? If it can, then would this lead to a drop in steam pressure but still allow the steam to heat the milk to the ‘correct’ temperature.

They are all good questions.

On my machine - and others I’ve owned - the VB closes as the temperature inside the boiler is around 100C. Last time I paid attention to that it was around 99C or 101C, I can’t remember exactly. I can let you know tomorrow when I make my morning coffee :-)

If the vacuum breaker were to open when you open the steam wand, you would hear and see steam coming out from the top of the machine, as if another steam wand would be open. I personally believe that what you describe is not possible, as, if there’s steam, then there’s water under pressure inside that boiler and the vacuum breaker will remain close. By all means though, take the top off your machine and check.

    PortafilterProcrastinator If opening the steam wand leads to a drop in pressure in the SB (which I am assuming it must) then can this theoretically lead to the VB opening?

    Not if the VB works. A vacuum breaker has one end of the circuit at atmospheric pressure (plus or minus tank depth pressure, but that’s negligible). For the valve to open, pressure on the other side of the valve has to be lower than atmospheric - which is what happens when a steam boiler that has been used (and thus is not full of water) cools down: the steam condenses and the water shrinks, resulting in a pressure below 1 bar, the VB opens and lets “whatever is on the other side of the VB” (air or water) in.

    If that were the case, the water in the boiler (liquid or steam) would be below atmospheric pressure, so definitely be cool…. but you wouldn’t get any flow through the steam wand, as the “open” end of the steam wand is at atmospheric pressure!

        CoyoteOldMan Thank you, again, makes perfect sense and see why my previous thoughts were wrong.

        I’ll be happy once I can get an accurate temp reading on the hot water, but looking like the sensor as temperature seems to be the prime suspect.

            PortafilterProcrastinator NTCs can be fickle. Looks OK, tests OK (in terms of electrical continuity/resistance at 20 °C), then you have a gas bubble or a crack in the potting resin and when heated it reads all over the place… at least it shouldn’t be expensive or difficult to replace!

                CoyoteOldMan CoyoteOldMan Thank you, really appreciate the advice.

                Paolo has asked me to swap the temp probes from each boiler over just to make sure nothing else is going on.

                Once he’s got back to me on the best way to get them out and whether I need to empty the boilers etc I’ll give it a go!

                    10 days later

                    I’ve not had a chance to look at the machine properly yet as there have simply been more important things going on in life, but I continue to use it daily for both espresso and lattes (well, hot milky coffee). Probably the reason for bouncing around in my head, frustrating I can’t just get on with it, but that’s life.

                    Following a saga with getting batteries for a sugar thermometer, I was finally able to better test the temp today. The highest reading I got (water running into an already hot milk jug) was 92deg. Boiler set to 130. However, see below - as this is a reading taken following a change in behaviour.

                    Interestingly milk steaming has been more variable. Certainly not what it used it used be. But. Beginning of this week I was steaming milk and there was a sudden and noticeable change in the noise and force of the steam. This was mid-steam. Milk was steamed better. But it varies still.

                    I have cleaned the steam wand a good few times with PulyMilk. The next step is to run some citric acid through the service boiler and then swap the temp probes over. I will hopefully get time to do this over the next couple of weeks.