Bezzera Strega cannot stop heating

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frankzs
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Joined: 3 months ago

#1: Post by frankzs »

Hi all,
I have been using strega for two years. One day last month, after the machine was turned on, it seemed to take longer to heat than before. When I felt that it was about to complete the startup process, the sound was louder than before, and white smoke came from the top of the machine, and there was a burnt smell. I was busy with other things at the time. After about two hours, I wanted to use it. I found that the power light was on, the yellow light was off, and there was a lack of water in the water tank. I refilled water, but the machine has no response, pump did not startpressure gauge shows 0, neither the steam switch nor the boil water switch responded.
I pulled down the lever and the pump started, and the water was hot, but soon the water temperature dropped.

I cut off power, opened the case, reset the temperature controller, and used a multimeter to measure the thermostat. It was fine, but the heating elements was burned out.
Later, I cleaned the two water level probes and now the water pump has restored water supply.

I judge that it may be due to a problem with the vacuum valve, causing the pressure to never reach the set pressure. The heating elements keeps heating, and finally the water is consumed, and the heating elements overheats and burns out.
But actually I am not sure whether the white smoke is coming from the vacuum valve or the safety valve.
Even so, I removed the vacuum valve and replaced a new o-ring seal inside.

I have ordered a new heating elements and have not received it yet, in the meantime I hope to find out what is causing the heating elements to keep heating.
I found the circuit diagram of this machine from the Internet.


From the diagram, the normally opened contact of the relay is connected to the heating elements, and the coil of the relay is connected to the pressure sensor and temperature controller.
I guessed that the heating elements continued to heat due to the sticking of the contacts of the relay, so I removed the relay and found that there were indeed traces of carbonization around the contacts, but the normally opened contacts were not stuck. Although I guessed that the relay could still be used,but I still bought a new relay of the same model and replaced it. It can be judged that the relay is not the cause of the continuous heating of the heating elements.

The newly ordered heating elements have not arrived yet, so I have not tested the effectiveness of the pressurestat.

Now I want to know if this machine has a water shortage protection mechanism (stops heating after water shortage)?
From the circuit diagram, it seems that the liquid level controller (control box or gicar) does not have the logic to control the heating elements.


I found a 220V light bulb, unplugged the wire connected to the heating elements and plugged it into the light bulb. At the same time, I took out the water tank, and then unplugged the low water level sensor. I hope to tell the control box that there is currently a lack of water in the boiler, and the water tank is too. I hope the control box can prevent the heating, but when I turn on the switch, the light bulb is always on, which means that the machine does not prevent the heating.
Is this normal? Or is my control box broken?

jamesz
Posts: 34
Joined: 2 years ago

#2: Post by jamesz »

frankzs wrote: I found a 220V light bulb, unplugged the wire connected to the heating elements and plugged it into the light bulb. At the same time, I took out the water tank, and then unplugged the low water level sensor. I hope to tell the control box that there is currently a lack of water in the boiler, and the water tank is too. I hope the control box can prevent the heating, but when I turn on the switch, the light bulb is always on, which means that the machine does not prevent the heating.
Is this normal? Or is my control box broken?
Try to unplug the other level sensor (mini level) and see what happens?
My understanding is that low level sensor tells machine when to fill the boiler while the mini level sensor controls the power to the heating elements.

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baldheadracing
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#3: Post by baldheadracing »

I don't have any solutions; just guesses.

I do wonder that when the boiler ran dry, why didn't the thermostat at the bottom of the boiler trip? That's why that thermostat is there; has it failed?

White smoke typically indicates to me burning plastic from excessive resistance built up in a connector (the cover burns) or within a switch or relay. Discoloured connector covers are always something to check for during the annual maintenance inspection, if not semi-annually.
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

frankzs (original poster)
Posts: 5
Joined: 3 months ago

#4: Post by frankzs (original poster) »

Try to unplug the other level sensor (mini level) and see what happens?
My understanding is that low level sensor tells machine when to fill the boiler while the mini level sensor controls the power to the heating elements.
Hi Jamesz,
Thanks for your reply,I thought the same as you, until now, I felt that this machine should work like this, but I unplugged the low water sensor, and the heating element still had a voltage of 220v.

frankzs (original poster)
Posts: 5
Joined: 3 months ago

#5: Post by frankzs (original poster) »

baldheadracing wrote:I don't have any solutions; just guesses.

I do wonder that when the boiler ran dry, why didn't the thermostat at the bottom of the boiler trip? That's why that thermostat is there; has it failed?

White smoke typically indicates to me burning plastic from excessive resistance built up in a connector (the cover burns) or within a switch or relay. Discoloured connector covers are always something to check for during the annual maintenance inspection, if not semi-annually.
I measured thermostat with a multimeter and it is on,I also don't understand why it doesn't get triggered after the temperature is too high,how to test whether it's reliable?

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baldheadracing
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#6: Post by baldheadracing replying to frankzs »

-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

frankzs (original poster)
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#7: Post by frankzs (original poster) replying to baldheadracing »

Yes, but I have to wait until the new heating element arrives :D

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baldheadracing
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#8: Post by baldheadracing replying to frankzs »

Why?
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

frankzs (original poster)
Posts: 5
Joined: 3 months ago

#9: Post by frankzs (original poster) »

baldheadracing wrote:With an oven? Spec is 135C https://www.bezzera.it/uploads/prod_ima ... .05_17.pdf
With an oven is a good idea :P ,you reminded me that I will find a soldering iron later, my multimeter has a function to measure the temperature so that I can remove the temperature sensor and measure if it works :D .

I also wanted to know if anyone who owns this machine has ever measured the voltage at the ends of a heating element when there is a shortage of water in a tank or boiler.