DIAGNOSIS The thermoblock heater is probably caked with mineral scale, acting as an insulator. It heats, but not efficiently or hot enough to produce a proper extraction temperature (195-205°F).
FIX You need to descale the internal thermoblock, not just run vinegar through the carafe. Use a liquid descaling solution (like Dezcal) made for single-serve/thermoblock machines. Fill the reservoir with the solution/water mix as directed. Run a full brew cycle into the carafe (without coffee). Discard that. Then run at least two full reservoirs of fresh water through cycles to completely rinse.
IF THAT DIDN'T WORK If descaling doesn't help, the thermostat sensor on the thermoblock might be failing, telling the board the water is hot when it's not. This requires replacing the thermoblock assembly, as the sensor is integrated.
HEADS UP Don't use granular citric acid or harsh vinegar concentrations for this. They can leave residues that worsen the problem or damage the small internal passages in the thermoblock.