DIAGNOSIS Mineral scale buildup inside the aluminum boiler. Scale creates hot spots that scorch the water. The charcoal water filter can't prevent hard water scale.
FIX Descale immediately. Use a commercial coffee maker descaler or a solution of one part white vinegar to two parts water. Fill the reservoir, run a brew cycle without coffee, then discard. Run two cycles with clean water to rinse. Repeat monthly if you have hard water.
IF THAT DIDN'T WORK The brewing temperature might be too high due to a failing thermostat. This is less common than scale. You'd need a multimeter to test the thermostat's resistance.
HEADS UP Never use abrasive cleaners or descale with straight vinegar. The acid can damage the aluminum boiler if left too long or used at full strength. Follow product timing instructions.