To avoid serious injury follow all warnings and instructions in the manual. Wear appropriate personal protective equipment.
Open electrical controls enclosure and turn switches to the off position.
Debris in valve diaphragm or plunger preventing spring-loaded closed function. Disconnect connector from valve solenoid cable. If temperature does not decrease, rebuild solenoid.
If the blue and red LEDs are on while heat is off, the Load Center board is bad. See Load Center Diagnostics in the system repair manual.