My brother NX-600 keeps displaying the code F04, if I switch machine off then on again it will allow me to sew, but then stops showing the F04 message agai.

"F04" appears on the LCD. ... If error message "F04" appears in the LCD while the machine is being used, the machine may be malfunctioning. Contact your authorized Brother dealer or the nearest Brother authorized service center.
https://support.brother.com/g/b/faqend.aspx?c=th&lang=en&prod=hf_inovnv180deas&faqid=faqh00100988_000

Any F messages on the machine indicates that the machine is malfunctioning. You will have to take it to a dealer to have it fixed usually.

http://www.sewingmachinesplus.com/brother-sewing-machine-error-codes.php

If you mean the foot controller, then the T/FC-322 is a substitute that should work. It's listed as a replacement here: http://www.sewingmachinesplus.com/234522001.php . The manual for the NX400 gives the foot controller as XC1154-051 . Brother changes the part number often but the wiring remains the same. Another substitute controller is available here: http://www.sewingpartsonline.com/foot-control-w-cord-brother-xc6651121.aspx .

The F04 message may mean there is an internal failure. This probably needs to be fixed by a Brother authorized repair person.

I wish that I had better news for you.

Cindy Wells

I had the problem with the error code F04 and found out that it is your foot pedal for the machine. Unplug it and it should start right up as ours did.You will need to fix or buy a new foot pedal. When they repair and or clean your machine they don't use your foot pedal but they use their own so they will miss the broken foot pedal.

I hope this helps you.
Bob

Did you check the manual? In the back it will outline what the number/code stands for. Do you have it in twin needle mode? If you don't have a manual, try going to the brother website to read the manual. You can go to my website www.112sewing.com and click on machines and it will take you right to brother. good luck

Call Brother at 1-877-276-8437 tomorrow. Your manual is available for free to download at www.brother-usa.com and see if it is listed on page 146. Hope it helps you Good luck, nothing more frustrating than a sewing machine being balky.

It most likely is your foot pedal. Unplug your foot pedal and start the machine without it. If it works properly without the foot pedal plugged in then your foot pedal needs repaired or replaced. This worked for us with the NX400 machine and I am sure the NX450 is closely similar. Don't bother to buy a Manual if you didn't already get one with the machine. A Service manual and parts manual is best; But just so you know they don't show the error codes unless you are a qualified and authorized repair person for the machines. I got my info from the repair man where my wife buys and repairs her machines. I am an electronic technician and mechanic so I understand how this system works. I will be repairing my wife's machines from now on.

Power off.

Remove the bobbin and bobbin case. Recheck the area around the shuttle for thread snips.

Power on.

If the problem continues you will need a professional to check the machine - It may need a more thorough cleaning than what the mfg allows the user access to or a new sensor.

I know this isnt of much help but my manual says that any errors starting with F is a sign of malfunctioning and should be taken in to a service center. Wish I could help more.