If you read what the manual says about that alarm, it indicates that the temperature probe has either opened or shorted. That's always a possibility. However, the way they determine that alarm could also mean the triac is shot. Also, there is a resettable thermal breaker on top of the boiler (red button on top) that could have either tripped or failed. So the first thing to do is push that red button and see if anything changes.
Essentially, the alarm is triggered either when the controller board senses that the boiler has gone over 140C, in which case it is likely that the overpressure valve on top of the boiler would probably be opening up and shooting water everywhere. Normally, after the coffee boiler heats up, the steam boiler turns on. Also, if the steam boiler temp doesn't exceed 60C within 5 minutes after the controller board commands it to turn on, you will get this alarm. That could be caused by a failed triac, a bad temp sensor, a bad heater element, or a bad thermal thermostat.
To narrow it down you need to check each item with a multimeter - either analog or digital. If you don't already have one you can get a cheap one that will do the job at most any HW store for $10-15.
1) Check the temp sensor by unplugging it (unplug the machine too for safety) and checking its resistance at the two wires going to the sensor while disconnected but still submerged in the boiler water. Depending on whether the water is essentially room temperature or somewhere between that and its normal operating temperature, you will see the range of values in the table below.
- PT1000 RTD Temp Sensor Chart.jpg (133.56 KiB) Viewed 8869 times
2) If the sensor checks out, next check the heater element with the machine unplugged. Disconnect the wires from each end of the heater element and check its resistance. it should read around 10 ohms. If this is OK and while power to the machine is off, check the resistance across the thermal breaker. It should be pretty close to 0 ohms if it is working properly. If that is OK and especially if it is not zero or a much higher value than 10 ohms, reconnect the heater element wires, plug the machine it, and turn it on. Switch the meter to the 125VAC range, wait until the coffee boiler heats and the steam boiler turns on (Boiler light on front starts blinking). Now check to see that you have 120V across the heater element wires. If not then it sounds like the triac is probably shot. Otherwise, it's probably the heater element, but in this case, you should have already seen an errant value previously when you checked its resistance.
If you suspect the triac you can always swap the two since they are identical. Just swap the wires if there is enough slack. If the triac has gone bad now the coffee boiler will not heat up. In this case after about 5min lights 20-21 should turn on indicating that the same problem as previously seen on the steam boiler has now been detected on the coffee boiler.
Let me know what you find out. At the age of your machine, I have seen equal numbers of users with triac, temp sensor, and boiler element issues so it could be any one of those!