Quick Mill QM67 intermittent steam boiler overheating

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
mycatsnameisbernie

#1: Post by mycatsnameisbernie »

I have a 2 month old Quick Mill QM67. It's the newest model with the dual manometer. I've noticed some intermittent overheating of its steam boiler. This only seems to happen after using the steam or hot water wands. I've never noticed it during initial warm up.

I have the steam boiler temperature set on the PID to 255F. I occasionally notice a steam temperature of around 265F. This would appear to be more than normal PID overshoot. When this happens, the boiler will cool down to 255F and then stay within 2 degrees of the set steam boiler temperature.

This morning, a few minutes after making a cappuccino, I heard steam escaping from the pressure relief valve, and the steam boiler PID temperature read 291(!). The steam pressure gauge was off the scale. The indicator light for the steam boiler heating element was off. I powered off the machine and let it cool off. It worked fine afterwards.

This afternoon, I was closely watching the machine after steaming. The steam temperature reading on the PID jumped suddenly from 255 to 265. When this happened, the steam pressure was about 1.7 bar; it's normally about 1.4 bar at 255. Again, the steam boiler cooled down, and operation returned to normal.

I'm thinking that the temperature sensor in the steam boiler might be intermittently reading too low, causing the steam boiler temperature to rise too high.

I will be reaching out to Chris Coffee for warranty service on Monday, but I'm wondering if this is a common failure mode in DB machines, and what the cause(s) could be.

Thanks for the help!

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cafeIKE
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#2: Post by cafeIKE »

Not exactly the same problem but Help! Quick Mill QM67 - no steam- steam boiler not heating up might have some useful information.

PID temperature jumps are either sensor electrical connection, defective temperature sensor, defective PID device in that order.

mycatsnameisbernie (original poster)

#3: Post by mycatsnameisbernie (original poster) »

Here is some more info:

I found I can reliably reproduce the problem just by steaming milk. With the steam boiler temperature set to 255, there is 1.4 bar pressure. As the milk steams, the steam boiler temp as displayed on the pid drops from 255 to about 245 and the pressure drops to 1.2 bar. After I shut off the steam, the temperature goes back to 255 but the pressure keeps rising to almost 2 bar, then the displayed temperature suddenly jumps to 265. Then everything cools down and normal operation continues.

I spoke to one of the techs at Chris this morning. They think that the SSR is intermittently getting stuck closed. They think the rapid 10° rise I am seeing could happen if the heating element were on continuously. So they are sending me a new relay. If that doesn't work, the next step will be to change the temperature sensor. I have no idea why making steam triggers the behavior.

If it were me, I might have tried things in the reverse order. In any case, I'll report back once the relay arrives and has been installed.

Stay tuned...

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cafeIKE
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#4: Post by cafeIKE »

If the temperature sticks @ 255 but the pressure keeps rising, the fault is the PID. It seems like it is displaying the setpoint and not the sensor temperature. SSR can't really 'stick'. If the SSR was sticking, the PID displayed temperature would rise right along with the pressure. [As an aside, I added a switch in my PID Vibiemme Domobar Super HX so I could toggle between PID and pressure stat. When ON, the displayed temperature matches the boiler pressure.]

I would ask for the PID reset instructions and reset the parameters. It could be the PID has glitched and has a parameter that is causing it to wind up.

If you get the reset and parameters, please post for the next guy.

mycatsnameisbernie (original poster)

#5: Post by mycatsnameisbernie (original poster) »

cafeIKE wrote:If the temperature sticks @ 255 but the pressure keeps rising, the fault is the PID. It seems like it is displaying the setpoint and not the sensor temperature. SSR can't really 'stick'. If the SSR was sticking, the PID displayed temperature would rise right along with the pressure.
The amber light that indicates the steam heating element is on never lights up as the temperature rises. The Chris tech said this light is connected to the input trigger of the SSR. So if the PID was incorrectly triggering the SSR, that light should be turning on.

Chris's theory is that the sudden rise of temperature is occuring during the several seconds when the PID is displaying the brew boiler temperature. By the time the display cycles back to the steam boiler temperature, the heating up of about 10° has occurred. Since the amber light never came on, the heating had to be caused by the SSR closing even though it had no input to do so.

I agree with you that this sounds very far fetched. But at this point I'm going to work with Chris on the diagnosis. The good news is that this problem only seems to be happening immediately after steaming milk. So I can work around the problem by turning off the steam switch immediately after steaming is done. Nice thing about the QM67 is that it has a separate physical steam switch - no need to navigate the PID settings to do it like on Profitec machines.

Thanks for the help and I'll update after I receive and install the replacement SSR.

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cafeIKE
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#6: Post by cafeIKE »

The brew boiler temperature should be nowhere near 255, more like 200°F according to the manual. The decimal dots indicate which boiler is being displayed.

From the manual:



Do you have the dual SSR or two single SSR?


While steaming, the trigger LED on the PID should be illuminated and should extinguish once the boiler reaches temperature.

What happens if you press both buttons to enter the programming mode when you have steam over pressure?

[DUMB idea having dual temperatures displayed. "Who's on 1st?" :roll: The PID should display the brew temperature and only show steam boiler temp when setting as the machine has a pressure gauge for the steam boiler.]

mycatsnameisbernie (original poster)

#7: Post by mycatsnameisbernie (original poster) »

Hi Ian

I guess I should have been clearer in describing what's going on.

My brew boiler is set to 200. My steam boiler is set to 255. When the machine is idle, the PID temperature display cycles back and forth between 200 and 255 (±1°). The cycle time is quite long. Each boiler's temperature is displayed for several seconds before switching to the other boiler. While the machine is idle, each boiler's amber light will occasionally briefly flash on and off as the PIDs keep the boilers temperatures constant.

When I steam milk, the displayed steam boiler temperature drops about 10° and the pressure drops. When I turn off the steam, I see the amber light stay on for a few seconds, and then it goes off. I will usually see the steam boiler display 255 with normal pressure about 1.4 bar. But during the next several second cycle while the brew temp is displayed, the amber light is stays off but the pressure continues to rise. When the display switches back to steam, it will show about 265.

Chris's tech's theory is that while displaying the brew boiler temperature of 200, the steam boiler SSR is briefly getting stuck closed, causing the steam temperature to spike. By the time the PID display switches to displaying the steam boiler, its temperature has increased by around 10°. Like I said, I think this theory is unlikely to be true, but at this point I have to go along with the tech's advice. It does seem to explain the behavior I am seeing.

I haven't taken the cover off my machine yet, but the tech told me I have 2 single SSRs, and he is sending me one.

The next time I steam milk I'll try pushing both PID buttons, but I expect it will enter the T1/T2 setting mode as usual.

Thanks for the help!

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cafeIKE
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#8: Post by cafeIKE »

Thanks for the clarification.

It's possible the SSR has a hold on failure.

Another possibility is the drive for the SSR & indicator lamp is slowly ramping down out of the PID. The indicator lamp may go out at higher voltage than before the SSR stops conducting.

When you get the cover off, determine which SSR is the steam boiler. Observe the indicator lamp on the SSR. When the fault occurs, i.e. boiler pressure increase, if the lamp is still on, it's the PID... or wiring.

bwren

#9: Post by bwren »

hmm... My QM67 EVO (2015) has a dual SSR - they've prob switched to 2 separate ones. Yes I agree that the oscillating temp display is a huge annoyance, as is the inability to disable the shot timer, which blocks the temp.

On a totally side note, I'm thinking of adding a flow control device from coffee-sensor to my QM67. Any experiences with this?

mycatsnameisbernie (original poster)

#10: Post by mycatsnameisbernie (original poster) »

Here's my update for today:

The replacement relay arrived from Chris today. Wow that was fast! Unfortunately I am away from home for 2 weeks, so I won't be able to install it for a while.

Next, before I left home today, I got to observe another overheat as follows:
  • Machine was idle, steam pressure 1.4 bar, displayed steam boiler temperature 255.
  • Displayed steam temperature suddenly dropped to 242, pressure remained at 1.4 bar.
  • Amber steam heating element indicator flashed and displayed temperature rose to 255. At the same time pressure increased to 2 bar.
  • After several seconds, displayed temperature jumped to 265.
  • The machine cooled off and resumed normal operation at 1.4 bar/255
At this point I am 100% positive that the relay is not the problem. But I exchanged emails with the Chris tech and he still wants me to change it and see if anything changes before he will send me a new temperature sensor.

Regarding Gavin's comments:

Here is the photo I received from Chris showing the latest version QM67 dual relays:


I got my machine with Flow Control installed by Chris. I also have FC on my other setup (Profitec Pro 500 w/PID). I use FC mostly to control pre-infusion. I find a long slow pre-infusion helps reduce channeling and helps to tame brightness of light roasts. Varying the pressure after PI is complete does change the flavor, but it is very subtle and not a game changer. Still, it's a lot of fun to play with.

Thanks for your help!