Aurelia boiler overfilling - need ideas
Long time lurker, first time poster.
I just wrote up the whole history of this problem and it ended up being a 3 page Word doc, so I figured I'd start with the basics and give more info when/if it's asked for.
Nuova Simonelli Aurelia volumetric 2-group has been overfilling and blowing the safety valve the past 2 weeks. The problem is intermittent, sometimes the autofill shuts off just fine, sometimes it just keeps going, and I think sometimes it starts filling on its own without the autofill cycle even starting up (can't be sure about that though)
Checked autofill probe, was fine, replaced anyway.
Checked inlet solenoid, seemed good, replaced inlet solenoid, rechecked inlet solenoid, seems good.
Repair shop said main board was fine.
Repair shop replaced brew buttons on right group, thinking that a janky taped-on button was messing with the electronics somehow.
Replaced safety valve just in case.
Stripped power cable and reconnected plug to be sure there's not a ground issue.
The boiler is still overfilling and burping from the safety valve.
Myself, the cafe owner, 2 trusted repair guys with a lot of experience, and the support people at NS are just about out of ideas. Little help? What would you try next?
Replies to This Discussion
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Permalink Reply by Scott on
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According to the Hydraulic diagram on Nouva's website, the pump feeds the steam boiler, so if that's the case, I'm doubting that 5 bar inlet pressure is going to affect the fill valve solenoid when the pump is pushing 9 bar. Unless this diagram is wrong or missing info-
http://nuovasimonelliusa.com/images/Technical_Information/Hydraulic...
What about a bad isolation valve to the boiler? It looks like there is one unlabeled in the diagram, next to the fill soleniod. It might leak into the boiler when the pump kicks on.
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Permalink Reply by Mike McGinness on
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When a steam boiler overfills from too high inlet pressure the issue is the valve opening when you don't want it open. 9bar sure you want it to open, 2 or 3 or 4 or in this specification case 5bar the valve should remain closed. Inbetween open at 9 and closed 5 or lower bar is when it can get dicey and open when not intended filling the boiler...
Scott said:
According to the Hydraulic diagram on Nouva's website, the pump feeds the steam boiler, so if that's the case, I'm doubting that 5 bar inlet pressure is going to affect the fill valve solenoid when the pump is pushing 9 bar. Unless this diagram is wrong or missing info-
http://nuovasimonelliusa.com/images/Technical_Information/Hydraulic...
What about a bad isolation valve to the boiler? It looks like there is one unlabeled in the diagram, next to the fill soleniod. It might leak into the boiler when the pump kicks on.
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Mike, the way the pump is plumbed - before both the inlet valve to the boiler and the groups, anytime the pump is running (fill solenoid open or not) there is 9 bar pressure against the fill valve plunger. That is what is happening when a shot is being pulled. So again not sure how high inlet pressure of say 5 bar is going to move the plunger in the fill valve, when said valve is under normal operation going to have to hold against 9 bar in normal operation. Then again I'm no Nouva expert. Maybe that's not the way it's really plumbed.
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Permalink Reply by Sam Cat on
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Brady-
Unit was purchased new in 2008. Last work done was descale last spring. Problem seemed to come out of the blue 2 weeks ago.
Water filtration is Optipure ScaleX-2, I know next to nothing about filtration so I'm not sure what that means as per your concerns. I change the filters every 6 months, last refresh was early October.
Backwards fill valve is, I guess, possible...I'll have to check it out tomorrow. I didn't touch it. If that was the cause of the problem, it would have been on backwards for months (if not years) before it let the boiler overfill, and the new valve would have been put on backwards twice by our repair guy...very unlikely. Manual fill valve is leak free.
Grounding came up with one of the technicians. I'm not sure about the boiler, but the second tech who looked at the machine last night was concerned about possible "bad" ground in the probe. He crimped the connection a little just to be sure. Probe itself was fine as far as we could tell but we had replaced it anyway a few days earlier.
We are NOT SURE it's an issue with the autofill valve. I don't know enough to rule out a cracked HX. Would there be any easy ways cross that off the list? I'm thinking the technician had that in mind when he said "your boiler is good," I'll get clarification tomorrow.
Thanks for the good questions.
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Permalink Reply by Brady on
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OK. After thinking more about this, I'm no longer worried about grounding of the boiler... it's connected via copper lines pretty solidly. I'm also not concerned about a possibly backward fill valve. Water is not really a concern given the system you're using.
Perhaps it would be helpful if you could describe what the machine is actually doing. Is the fill system behaving strangely or is the machine just overfilling and it isn't clear why? That will narrow things down.
A leaky heat exchanger will lose pressure on the brew side after water is shut off, though there are other leaks that will do that too. A leaky heat exchanger will also overflow the boiler like a leaky fill valve. Kind of hard to isolate.
I do still wonder about that probe wire. I'd wiggle that along its length to see if I can get the fill circuit to run.
Keep us posted.
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Permalink Reply by Mike Sabol on
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You might need to disconnect the fill valve from the boiler and watch it's behavior. (Look for small leaks, unit passing water when it shouldn't, solenoid on when it should be off, etc) You can't really troubleshoot unless you know where the water is actually coming from.
A cracked hX would lead to a more consistent and gradual overfill and would continue to fill the boiler even when powered off.
Whenever I encounter a head scratcher like this one I always try and back up a few steps and look at the problem from as general a point of view as possible. And I don't think in terms of specific parts or describe the problem as a particular part being bad. That just leads to "part changing". I try to think in terms of the general system at issue instead. The issue in this case is that water is getting into the boiler when it shouldn't be. Which is the cold water inlet system. Since there are multiple points inlet water can enter the boiler you have to figure out which one is letting the water in.
Once you know which point is leaking then you can address the specific mechanical and electrical controls associated with that point.
I'm not trying to be flippent but I know from experience that sometimes people will put more energy into being amazed or frustrated at a mystery problem than into actually working the problem. I've done it many a-time myself.
Personally, my money is on a bad ground to the boiler. Perhaps a wire break inside the insulation between the board and the boiler. If some other electrical device was shorted with extremely high resistance to ground and allowing the ground to have a bit of voltage you would "confuse" the board. Elements can do this. Checking resistance on the element would tell you if that was the problem.
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It has actually been very very difficult to pin down what exactly the machine is doing. There is no pattern or regularity to the failure that makes it possible to predict when it will happen and be ready to observe, or any method to intentionally cause the failure.
Whenever the boiler begins to fill and doesn"t stop, it fills rapidly. Whether or not it turns out that the extra water is coming through the autofill valve or somewhere else, the boiler fills at a similar rate to a normal probe-regulated autofill cycle. As I said to Mike, it probably about 30 seconds from the time I hear the boiler begin to fill (and see the level gauge begin to rise) to the time the boiler is full enough to pop the safety valve. You can watch the pressure needle slowly fall as the boiler fills and then spike back up 1-2 seconds before the purge. I have left both wands open (water into the drip tray) while this is happening and it has continued to fill/empty through the wands for up to 30 seconds (might go longer but that's when I shut the machine off) without blowing the safety valve. Hitting the power switch has stopped the filling 100% of the time.
I can say with confidence - not certainty - that the overfilling has begun while the pump is off. It has begun at the end of the night when the machine hadn't been used for 20 minutes (according to staff), and I've personally seen it start to fill over 1 minute after the last shots were pulled and groups purged, after the normal autofill had started and stopped normally.
I don't know if the overfilling has ever begun while the pump was on. Not anytime I've been on the unit.
Occasionally the autofill will cycle on/off/on/off in short bursts, I've always attributed this to the fact that our machine has long legs and sways a little when the portafilters are manuevered (water level rising and falling on the probe). When we "swivel tested" the probe there was a .5 - 1 second delay before the autofill turned on/cut off.
I think the rate of fill is important here. When you use the word "leaky" I read it as slow drip, 1/4 or less of normal flow. Is that about right? We've got sudden, heavy flow into the boiler that shuts off when the machine is powered down.
I'm hesitant to mention this in case it throws us off track of the issue at hand, but if it turns out to be a brain issue maybe they're connected. We actually had a problem after our new autofill valve was installed with the boiler not filling the next morning. Got hot enough to melt the heating element cover mounts a bit. After it was removed, inspected (nothing), and replaced, it didn't happen again.
???
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Well at this point the machine is a few hours away and out of my hands. I'm sure the folks working on it are isolating the variables as you suggest instead of just slapping on new parts until something works. We may done a little of that with the new probe and valve, but those seem to be the most common causes of a problem like this so I'm not feeling too rough about it :) And I can't speak for the service and repair guys involved, but as far as I'm concerned you're exactly right about enjoying the frustration more than is efficient! Obviously my experience inside my unit (and espresso machines in general) is hardly extensive, so every problem is an opportunity to learn something new. Chase a lot of rabbits down a lot of holes, but for now that's how I'm learning...
Mike Sabol said:You might need to disconnect the fill valve from the boiler and watch it's behavior. (Look for small leaks, unit passing water when it shouldn't, solenoid on when it should be off, etc) You can't really troubleshoot unless you know where the water is actually coming from.
A cracked hX would lead to a more consistent and gradual overfill and would continue to fill the boiler even when powered off.
Whenever I encounter a head scratcher like this one I always try and back up a few steps and look at the problem from as general a point of view as possible. And I don't think in terms of specific parts or describe the problem as a particular part being bad. That just leads to "part changing". I try to think in terms of the general system at issue instead. The issue in this case is that water is getting into the boiler when it shouldn't be. Which is the cold water inlet system. Since there are multiple points inlet water can enter the boiler you have to figure out which one is letting the water in.
Once you know which point is leaking then you can address the specific mechanical and electrical controls associated with that point.
I'm not trying to be flippent but I know from experience that sometimes people will put more energy into being amazed or frustrated at a mystery problem than into actually working the problem. I've done it many a-time myself.
Personally, my money is on a bad ground to the boiler. Perhaps a wire break inside the insulation between the board and the boiler. If some other electrical device was shorted with extremely high resistance to ground and allowing the ground to have a bit of voltage you would "confuse" the board. Elements can do this. Checking resistance on the element would tell you if that was the problem.
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Thanks Sam, that description helps out a lot. So, I think we can be pretty sure the issue is with the fill probe/circuit. It would be interesting to know how that other fill valve coil failed - open, short or other resistance value failure; or something mechanical (you didn't actually say what the nature of the failure was). It's possible the valve coil damaged the driver on the board. And now that driver is presenting an random/intermittent failure. I've seen this exact failure on other makes of equipment that I've worked on. Bunn brewers ,specifically, come to mind.
I'm hesitant to mention this in case it throws us off track of the issue at hand, but if it turns out to be a brain issue maybe they're connected. We actually had a problem after our new autofill valve was installed with the boiler not filling the next morning. Got hot enough to melt the heating element cover mounts a bit. After it was removed, inspected (nothing), and replaced, it didn't happen again.
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There is definately something wrong with the fill circuit. Cutting the power and having the issue stop right away is a good indicator that the brain is telling the valve to open when it shouldn't. Which means the water detection circuit is getting interrupted somewhere. Like I said earlier my money is on a bad wire between the board and the boiler. They can do simple continuity tests to check. Otherwise Scott is on to something with his bad brain. (And I know the Bunn Brewers of which he speaks.)
My longshot idea is the heating element shorting with very high resistance to ground and leaking voltage into the ground circuit. This would affect the way the brain keeps track of the fill probe and would happen whenever the element fired. The Aurelia element actually has three elements on it that are tied together with little copper jumpers. In order to check for this condition the techs would have to disconnect the element and remove the jumpers and then test each element separately. They should each have an Ohm value somewhere in the mid 20's. If one registered in the mega-ohms that would cause a small leak to ground but not enough to throw the breaker and would also mess with the fill circuit. I doubt this is the case but checking for it is cheaper than buying a new brain. You want to be sure that replacing the board is going to solve the problem before you buy it.
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This narrows it down in my mind. Fill system electrical issue. Probe wire, voltage weirdness, or bad board.
Sam Cat said:...I have left both wands open (water into the drip tray) while this is happening and it has continued to fill/empty through the wands for up to 30 seconds (might go longer but that's when I shut the machine off) without blowing the safety valve. Hitting the power switch has stopped the filling 100% of the time.
I think the rate of fill is important here. When you use the word "leaky" I read it as slow drip, 1/4 or less of normal flow. Is that about right? We've got sudden, heavy flow into the boiler that shuts off when the machine is powered down.
I'm hesitant to mention this in case it throws us off track of the issue at hand, but if it turns out to be a brain issue maybe they're connected. We actually had a problem after our new autofill valve was installed with the boiler not filling the next morning. Got hot enough to melt the heating element cover mounts a bit. After it was removed, inspected (nothing), and replaced, it didn't happen again.
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