# Cimbali M21 Overpressure issue



## Acanthodian (Sep 25, 2014)

I am at my wits' end on this fault, so any help will be greatly appreciated.

The machine is a 2007 but is very little used (due to the problem below) in a domestic environment.

It has a tank and I have used Volvic water for some time

It is now on its 5th Pressurestat (2 Cimbali and 3 CEME 5612) although have come to the conclusion it is nothing to do with the pressure stat.

It can behave perfectly for weeks but then after being on for 40 minutes to 1 hour it will go over pressure and trigger the safety valve. Releasing pressure via steam wand or hot water may or may not get it behaving again.

When going over pressure the pressurestat make the usual audible click and there is a 1-2 second lag in the pressure build-up, but the pressure just keeps building again

I should add there is no obvious sign of boiler overfill (which to me, is steam from wand is dry when going over pressure) and I have twice replaced the level sensor in the boiler.

Looking online, similar issues do seem to be associated with boiler overfill (but with obvious signs). While I do not want to waste cash, do you think it worth just getting a new 2 way fill solenoid (I assume it is number 26 in the cafeparts page below)?

http://www.cafeparts.com/Espresso-Machine-Parts/Cimbali/Water-Inlet-Tap-M21-junior

As an update: I just disconnected the wires to the pressurestat (while it was operating normally)and unsurprisingly the heating element stayed off and the pressure dropped. Some time later when the machine went over pressure I repeated this (completely disconnecting wires to the pressurestat)but it had no effect (heating element remained on and pressure continued to build).


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## ajohn (Sep 23, 2017)

Looking at the boiler parts list you have an electronics box. I couldn't find a wiring diagram but the chances are that the pressure switch goes to that and something in that drives the heater. That would fit in with your update.

Maybe they use a relay to drive the heater. Sometimes contacts stick for a variety of reasons. Or it could be a problem with what ever drives the relay if that's what they use. Same if they use something else such as an scr arrangement but in that case it' probably what ever is driving it.

I'd suggest you trace the wires and see where they go and what to. It sounds like the pressure switch doesn't drive the heater directly.

Excuse me - Rather than mention SCR. If heater switching is done electronically and no relay it's more likely to be a triac.

John

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## El carajillo (Mar 16, 2013)

Check under the drip tray between the electronics and the contactor, look for a grey wire, apparently this carries the signal to the fill probe.

If it get pinched / damaged it can create the problem you have. CHECK ALL CONNECTIONS

Also check the pipe to the pressure stat is completely clear.

Noted on Home Barista


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## Acanthodian (Sep 25, 2014)

Many thanks for your reply. The wires from the pressurestat lead to the electronic control board. Switching of the heating element is indeed done via a triac ( the third 'signal leg' coming out of a 'microchip', which must somehow connect back to the pstat). I switched out the triac for a new one but the damn thing just went overpressure again.

I ran the machine with the pressurestat disconnected and there is plenty of steam getting down the pipe. Also the experiment of electrically disconnecting the pressurestat and seeing the heating element still on, strongly implies it isn't a psat issue.


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## Acanthodian (Sep 25, 2014)

Having scoured the forums for similar M21 issues, completely agree overfilled boilers seem to be the culprit.

My only thought is the machine doesn't show signs of overfill, ( dry steam etc) although never having had an overfilled machine I am not 100 pct sure. Will have a look for the grey wire now! Thanks


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## ajohn (Sep 23, 2017)

The pstat will go to the electronics as well by the sound of it. If you put a voltmeter across it you should see some volts very probably when it's open and close to or zero volts when it's closed and active. Any even cheap dvm should be fine for this. That should tell you if the stat is working correctly. The volts might be the other way round.

Seeing what is going on with the triac is a bit more difficult but you will have mains volts across the heater when it's on a little when it's off. You need the AC voltage range for that. The pstat is probably DC.

The meter wont care much which it's set to just give stupid readings if it's the wrong one especially on AC when it's trying to measure DC,

John

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## espressotechno (Apr 11, 2011)

If the boiler is overfilling, you'll get water coming out of the safety valve, not steam.

You may well need a new electronic control box: What's the Gicar code on the old one ?


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## Dylan (Dec 5, 2011)

Why would an overfilled boiler cause the problems described?

When the pstat clicks on it closes its circuit activating the element, when it clicks off it opens it turning off the element. Afaik there are no other parts in an espresso machine (other than the Gicar the circuit is attached to) that are able to override this basic circuit.

So... if you have observed the boiler gaining too much pressure and whilst it is doing this disconnected the pstat to open the circuit and it yet the element remains on this would indicate a short circuit or much more likely a faulty Gicar.

Happy for someone to point out a flaw in my thinking here, but I cannot see how a over filled boiler can override the pstat.

Edit: Unless the machine is activating its pump after it has heated up and pumping water into the boiler - this would obviously cause over pressure and the safety valve to vent. Is the pump active when this problem occurs?


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## espressotechno (Apr 11, 2011)

*PS* Also the RL number on the Gicar box.


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## Acanthodian (Sep 25, 2014)

Dylan,

We definitely share the same conclusion.

There is no sign of overfill (no water coming out of safety, no pump activating(other than when drawing hot water as expected) and the volume of water coming out of hot water tap is not enough to completely fill the boiler)

Think it has to be a faulty GICAR (no other way to explain the behaviour when disconnecting the psat in over pressure scenario). Have changed the triac (not that) and looked under the microscope for shorts/poor connections on the PCB.

The question is new GICAR (ouch) or just connect the Pstat to a new SSR that controls the heating element (taking out the GICAR and TRIAC )but leaving the Thermal cutout (not on the GICAR) in the circuit.


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## Acanthodian (Sep 25, 2014)

espressotechno said:


> *PS* Also the RL number on the Gicar box.


It is CBL555


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## espressotechno (Apr 11, 2011)

PM me the Gicar code and RL number and I will give you a price for a new ECU.

If your machine is a semi-auto, a new ECU may be quite cheap...


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## ajohn (Sep 23, 2017)

If the circuit board is brownish rather the greenish and definitely not fibreglass there are couple of things you could try if it is the electronics. Paxolin / paper based is usually brown and dirt cheap. It's famous for having dry joint problems due to moisture in it when the boards are soldered. The cure is to use a lightly wetted soldering iron on the joints. If there is moisture in the board there will be spitting and popping. Best option in that case might be to bake it at say 40C for a few hours. Fibreglass boards shouldn't have that problem but can still have dry joints. Sometime if there is a lack of solder on a joint it's best to add a bit more but if there are any really fine lead pitched parts it needs fine solder and a stereo scope - even for retouching joints really.

One thing that could happen on items like this is a problem on the pstat. It might have initially been made to switch high currents and AC. Along comes electronics, low current and very probably dc and the contacts passivate. That's why I suggested checking it with a dvm to make sure it really is switching cleanly. Passivation makes contacts appear open circuit or rather resistive so can result in all sorts of results. The best fix is gold plated contacts especially if the current is just a few ma.

Triacs can fail open or short circuit and probably some state in between but I'd say that was unlikely. Again the best check is a dvm. They should only have few volts across them when on and something truly low across the heater when they are off. There should only be ma running though it at the most when it's off but I wouldn't suggest that you check that with a meter.

John

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## espressotechno (Apr 11, 2011)

Code CBL555 (442-638-020) indicates that the ECU is not a Gicar one.

Ouch ! A new one is very expensive (approx £350), and available only to order.

Your ECU may be repairable: There are several pcb repair companies who could repair it for around £100. (I use a company near Bradford).


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## Acanthodian (Sep 25, 2014)

John

Many thanks for the ideas. It is green fibreglass board. I have had it under a 400x mag microscope looking for bad joins ( it was good). This problem has been there for a cool 5 pressurestats ( the problem appeared within an hour of putting the last CEME in ( which prompted the unplugging experiment).

changing the Triac had no effect but I will meter the connections

QUOTE=ajohn;537340]If the circuit board is brownish rather the greenish and definitely not fibreglass there are couple of things you could try if it is the electronics. Paxolin / paper based is usually brown and dirt cheap. It's famous for having dry joint problems due to moisture in it when the boards are soldered. The cure is to use a lightly wetted soldering iron on the joints. If there is moisture in the board there will be spitting and popping. Best option in that case might be to bake it at say 40C for a few hours. Fibreglass boards shouldn't have that problem but can still have dry joints. Sometime if there is a lack of solder on a joint it's best to add a bit more but if there are any really fine lead pitched parts it needs fine solder and a stereo scope - even for retouching joints really.

One thing that could happen on items like this is a problem on the pstat. It might have initially been made to switch high currents and AC. Along comes electronics, low current and very probably dc and the contacts passivate. That's why I suggested checking it with a dvm to make sure it really is switching cleanly. Passivation makes contacts appear open circuit or rather resistive so can result in all sorts of results. The best fix is gold plated contacts especially if the current is just a few ma.

Triacs can fail open or short circuit and probably some state in between but I'd say that was unlikely. Again the best check is a dvm. They should only have few volts across them when on and something truly low across the heater when they are off. There should only be ma running though it at the most when it's off but I wouldn't suggest that you check that with a meter.

John

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## Acanthodian (Sep 25, 2014)

Thanks. I want to bypass that function on the board with a new SSR but my wife thinks I will burn the house down! I will follow your advice and send it to a PCB repair place I have used in the past



espressotechno said:


> Code CBL555 (442-638-020) indicates that the ECU is not a Gicar one.
> 
> Ouch ! A new one is very expensive (approx £350), and available only to order.
> 
> Your ECU may be repairable: There are several pcb repair companies who could repair it for around £100. (I use a company near Bradford).


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## espressotechno (Apr 11, 2011)

Let me know if the PCB repair was successful.


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