When printer doesn't heatup, it could be that the the printer went in standby mode to save power. Only applicable to FELIX 3.1 and older.

To get printer out of standby mode do one of the following.

1. Please press "on/off" button twice in repetier-host interface. or on display unit
2. Press emergency stop button 
3. Disconnect and then re-connect printer.

When heater decoupled message or DEF or DEC is displayed on the screen, this means that a heater element or thermistor is broken or not mounted right/loose.

DEF: Thermistor circuit of respective heater is defect. The controller measure a temperature below 5 degC or 300degC.
DEC: Heater circuit cannot hold temperature within 20 degC or temperature cannot rise fast enough to target temperature. (for extruder 1 deg within 15 seconds, for bed 1 degC within 60 seconds)

DEF and DEC are generally caused by:

1. Wiring is defect. Wiggle cables and see if message appears. Move axes over full range and see if message appears at a certain position.
2. Wires are not correctly mounted on control board of printer. Check if wires are correctly placed on the screw terminals or plugs on the mainboard.
3. Thermistor and heater not correctly mounted in heater body. Check if thermistor and heater are properly fixed in the heater body of the hot-ends
4. Switched thermistor or heater in case of dual head.  Make sure heater 1 correspond to thermistor 1. Just heatup heater 1 and check if heater 1 actually rises in temperature.
5. Thermistor or heater element itself are defect. Replace element and check if it resolves issue
6. Control board is defect. Least common is that mainboard is defect. Replace mainboard

FELIX TEC/3.x specific common causes:
Static electricity.
Printers and thermistors delivered before 2015 showed in some cases fast fluctuating temperature readings causing a DEC error. This was caused by static electricity buildup influencing the temperature measurement.
When does it happen.

• Only happens for extruder temperatures
• Happens when the top cable loop with cable spiral is touching the aluminum frame and the thermistor wire is touching the cable spiral

Solutions:

• Replace therimstor wire with better insulated ones 99% of the times solves the issue. These are delivered after december 2014. If you don't want to buy new thermistor or are in urgent need. You can also use next tips.
• Make sure the top cable loop is not touching the aluminum frame.
• Put felt tape around the cables inside the cable spiral.
• Remove the cable spiral and for extra certainty make sure the wires of the top cable loop aren’t touching the frame.
• Make sure you have the latest firmware loaded for your printer, containing better temperature values.

FELIX Pro specific common causes:

Extruder

1. The thermistor/heater wire is not correctly plugged onto the extruder PCB.
• The white big connector of the hot end should be plugged all the way onto the PCB. 
• Make sure connector is not plugged backwards. The internal contacts should touch the contacts on the edge of the extruder PCB
2. The contact pads on the edge of the extruder PCB are not clean. In some cases the isolation material applied during the production process is not properly removed causing bad electric conduction. Clean contacts with methylated spirit.

Heated bed

If you get a DEC or DEF message in front of the heated bed icon on the display, please check the following things:

1. Is the bed correctly placed on the magnets, according to instructions.
2. Check if the contact points underneath the heated bed are clean and free from burnmarks
3. Check if connector pins are not damaged.
4. Check the magnet of the heated bed that is closest to the connector. In rare cases it breaks loose out of the bed and then it can be pulled out, causing disconnects (because the bed is not close enough anymore to the pins). Also measure how far that same magnet sticks out above the bed bottom. This should be around 2.5 mm
5. Check wire breakage in cable loop under bed. Wiggle cable, while heating or when idle. If the temperature fluctuates or heating stagnates, there is most likely a wire breakage. Another way to test this is by moving the bed (y-axis) to several positions and check heating behavior.