Hi all!

I have been lurking around for a while and i hope my first post was under different circumstances! Possibly with your expertise i will be posting about less agonizing stuff in the future.

To the point; I bought a used Isomac Millenium a few days ago and i think what i experience is not a normal behavior (i'm new to HX machines so i am not sure)

As you can see in the video below the boiler pressure seems to cycle too fast in my belief. It maxes out at 1.3bars and then starts going down immediately. Min pressure is around 1.1 when the heating element kicks in again. This goes on forever. In the video the machine was on for 40min already.

I assume that this should not be the case when the machine is idling and the pressure should be relatively constant around 1.3bars. Isn't that so?
/John

Well, I don't own this machine or any machine with pressure gauge, but it's normal unless you have a PID.
You can hear thermostat switching on at 1.1 bar, which is around 122°C, and switching off at 1.25 bar, which is around 124°C, then the pressure rises to 1.3 as the heater is still hot, so water warms up slightly more, and then gradually cools down until next heating cycle

Leaky anti-vacuum valve. Change the o-ring.

Alan

Hi Alan.

I don't think this is the case here. The anti-vacuum valve doesn't hiss at all (after a few seconds of the initial startup).
I tried the chrome spoon method on the anti-vacuum valve and i can't see any fogging. Here's how the setup looks like (mind that in the picture the machines is cold so the valve is not at its' "high" position) :



I'm just wondering if the cycling is happening too fast here. It's a 2-3 celsius degree temperature change between 1.1 and 1.3bars but should this happen so fast? The pressure gauge upon reaching the 1.3bar mark immediately starts dropping and in 40sec it's back to 1.1.

/John

I assume that this should not be the case when the machine is idling and the pressure should be relatively constant around 1.3bars. Isn't that so?

No.

The action of the thermosyphon system (primarily) and the heat loss from the boiler casing cause the steam to condense (pressure falls) and the cycle repeats over and over. 40 seconds after 40 minutes SEEMS short so there must be a small leak somewhere.

Jsub wrote:It maxes out at 1.3bars and then starts going down immediately. Min pressure is around 1.1 when the heating element kicks in again

Pressurestats typically have a deadband (delta between on/off) of 0.2 bar. How much time between the top and bottom of the cycle depends on heat loss. If there's a leak, of course that will shorten the cycle time. Well insulated steam boilers have cycle times of a few minutes; poorly insulated ones will cycle approximately once a minute.

It doesn't apply to the mechanical pressurestat on your Isomac, but for sake of completeness, electronic temperature controllers ("PID") have a much smaller deadband of 0.1 degrees and they will cycle the heating element every few seconds for a brief blip.

@Eric, Thanks for the detailed explanation.

The graph is really helpful to understand what is the expected drop in pressure.
Although not the same machine (so heat loss won't be the same) the pressure drop in your graph is 0.15 bars in 100sec period which seems more logical to me. Extrapolating, it would be around 22min for a 2bar drop in pressure.

@Dan. I am fairly familiar with the internals of a pstat so i understand your point. Also, i have PIDed an older machine of mine so i am also familiar with the concept. It's good you mention it though, for the sake of completeness as you stated.
Just wanted to verify here that for the specific boiler this was not the expected pressure drop "curve", indicating that there is a potential problem.

Any idea on where the leak might be or how to go about detecting it?

Something i failed to notice is that the solenoid valve doesn't look in good condition so i am planning to try and clean it or change it. But could this cause an effect like this (fast drop in temperature/pressure)?


/John

Could be. Pressurestats also tend to have an ever increasing deadband as they age but your machine is cycling a bit of the fast side which as others have pointed out is usually a result of a small leak somewhere. Check the steam wand as well. I had a Millenium long, long ago and had to replace the valve gaskets after a year or two of use.

I think that the culprit might be the solenoid in this case.
I removed it and it's bad. The barrel where the shut-off valve is seating in, has a crack. I wonder what caused this failure?



Since this is a normally closed valve, the barrel seems to be directly connected to the boiler in this machine. I would expect a constant leak but that was not the case or at least it was not visible.

I will change the solenoid and come back with the results.

Since i undid a lot of the plumbing, here is my custom boiler descaling technique! Overfill from the top, wait 2h, drain at the bottom



/John

Hi John,

I'm curious if you were able to attribute your rapid heating element cycling to the solenoid valve? I'm having similar problems and have eliminated the vacuum breaker as a culprit.