1 month old La Marzocco Linea Mini triggering thermal switch daily

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

#1: Post by Alestz »

Hey guys,

I bought a new Linea Mini about a month ago and everything has been working great. In the last week or so, the thermal safety switch has been getting tripped several times everyday. This requires me to open up the machine in order to reset the switch manually. I have been in contact with Chris from LaMarzocco and he said that a tech can come out to me after New Years. Is there anything I can do to diagnose it in the meantime? The machine seems to work most of the day, but about 30 min after finishing a shot, I hear the switch trip and heavy steam comes out of the group head when the paddle is switched. I have been using the machine to make about 5 shots a day for the past month at brew temperatures from 197-202f

Any advice or similar experiences?

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#2: Post by Marcelnl »

I assume the machine does have a pressurestat? Almost sounds as if it is 'sticky' and makes the boiler overheat. If you have been in touch and did not get any further instruction I'd stick to swicthing it off after use, nuisance and all, until that tech comes out. Ultimately that thermal switch is your second safety measure to prevent extreme overpressure/catastrophe, the overpressure valve is the last.
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Alestz (original poster)

#3: Post by Alestz (original poster) »

Thanks for the reply! Yeah, the machine does have a pressure stat. The machine seemed to work fine this morning when I made 3 shots. I am semi-concerned something is off even when the machine is usable from a thermal safety switch not tripped perspective - my shots are running a lot slower than usual when set at 200f despite changing my grind to a non-standard (to me) espresso grind range. The shots taste a bit watery and acidic, but if the shots are running so slow, I am not sure I want to grind finer and bumping up the temperature has it's own problems given the machine's potential problem...

Alestz (original poster)

#4: Post by Alestz (original poster) »

update: a tech came and replaced the high temperature thermostat and potentiometer in the beginning of January which resolved the problem for about a month. Earlier this month (February), the overheating started happening again so I contacted Chris again. The plan now is to replace the temperature probe which is currently underway at the tech's local shop

This is very unfortunate how many problems I have been having despite it being a new machine. The customer support seems superb even though it shouldn't be necessary this early on in the machine's lifetime

Will update this thread if the machine has issues after I get the LMLM back post temperature probe replacement


#5: Post by vansover »

@Alestz - any updates? Looks like almost 4 months passed since February - was the temp probe indeed replaced? Did the issue of the safety switch triggering disappear/get resolved?

I'm trying to troubleshoot what seems to be the same issue. The thermal switch on my LMLM trips occasionally - when it does, it happens only when turning the machine on. It never tripped for me if the machine is already at operating temperature.

Scott tried to assist me as well. We replaced the PID's potentiometer, replaced the safety switch (twice), upgraded the control module to the "connected" version - nothing helped :(


#6: Post by JRising »

vansover wrote: I'm trying to troubleshoot what seems to be the same issue. The thermal switch on my LMLM trips occasionally - when it does, it happens only when turning the machine on. It never tripped for me if the machine is already at operating temperature.
What you're describing is a safety thermostat on its way out. Every time it switches, it makes a little spark and deposits a little carbon. When heating from cold, the power is on for several minutes straight and this carbon heats up and heats up until the switch triggers itself, not the boiler overheating and triggering it, but the heat generated in the safety itself by bad contact and the full 1000+ watts of element power passing through that carbon. Once the boiler is warmed up, the 1000+ watts is only on for several seconds at a time, keeping the boiler stable and the heat inside the safety is able to conduct away through wiring. I'd replace the safety T-Stat.

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#7: Post by BaristaBoy E61 » replying to JRising »

I would replace the T-Stat as John suggests and I would also install across the T-Stat leads a .01mfd 1000v Ceramic Disk Capacitor to attenuate or completely eliminate the 'Sparking' or 'Arcing' phenomenon after speaking with LM technical services to discuss this matter to get their input and approval.
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#8: Post by JRising »

Barista Boy isn't wrong. But once replaced, that new Safety T-Stat should go many years without switching, so the carbon building thing will be quite a distant future thing.


#9: Post by vansover »

JRising wrote:... the full 1000+ watts of element power ...
Thanks for the idea and thought. And sorry - I think I failed to mention that the safety switch failing on my LM is the the one located on the espresso boiler (not the main boiler). This safety switch gates a much more humble 250W heating element - not the >1000W one used by be steam boiler.
Also, this element is controlled by the PID - now, admittedly, when coming from a cold state, the PID will generally command longer periods of "ON" but even then, I believe the "ON" periods should be shorter than 10 seconds.


#10: Post by JRising »

I still think it's a bad t-stat, triggering off of it's own generated heat. You could measure the resistance across it when the boiler is hot. Ie. Let the machine heat fully, unplug the machine, check resistance across the safety... Even 0.4 ohms is a heck of a little heater.