I had that problem with my cpa2. The capillary thermostat was dead. I looked around for a replacement, gave up and soldered up an electronic replacement made up of an op-amp, relay, pot and a sensor recycled from an old grill thermometer. It works fine for me, just the numbers on the dial don't match actual temperature - nothing that a sharpie could not fix.
You can contact cat-labs and see if they have a spare - this might be the easiest way to go now that JOBO is alive again
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