Temperature probe - water saturation and protection

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glendeni
Posts: 1
Joined: 8 years ago

#1: Post by glendeni »

I didn't find anything describing my specific problem when trying to analyze and fix it so in its aftermath wanted to post in case someone else encounters same. My problem was water being trapped in a temperature probe, how it was manifested, and what it took to fix.

I have a Bezzera Unica with temperature probe mounted atop the boiler, its wires extending vertically and connected to a PID. Recently while descaling the machine I accidentally spilled some water on its top cup warming tray. Awhile later "A2" appeared in my PID. An on-line search indicated a low resistance value - possibly from a short or an unexpectedly high temperature.

Opening the machine up, I found water had dropped through the top plate holes into the well of the temperature probe, from which the wires extend, filling it - my "A2" was resulting from conduction through the electrolyte-laden water. So I placed the machine on its side, to let the water leak out, and had a fan continually blow air over it.

This went on for a whole week - periodically uprighting and testing it would produce an initial warming and then the target temperature - but sooner-or-later the "A2" would appear and the machine would cool down.

After the first four days with no success I ordered a new probe, but continued the drying process. But on the very day that the new probe arrived the machine finally was able to maintain the target temperature. So it took an entire week to recover, despite continual airflow over the probe (and I later wrapped a heating pad around the boiler to aid the evaporation). But it did recover eventually.

I left the machine on for a day afterward so the hot boiler would help dry out any remaining moisture. Then I added some heat shrink tubing around the probe wiring, large enough to cover the attaching bolt, with an upside-down "U" shape so water should not get into the probe well again, even if water drips through the top holes. The basic problem is that without any protection, water reaching the probe will be caught inside and be very difficult to extract.

jonr
Posts: 610
Joined: 11 years ago

#2: Post by jonr »

> I accidentally spilled some water on its top cup warming tray.

IMO, machines should be designed with this in mind. Ie, assume that water will by spilled/leaked/sprayed throughout the entire machine and design sensitive items to shed water and drain to the counter (not be trapped under the base like my slightly rusted Europiccola).