A320 CREW HAS HOT BRAKES ECAM AFTER TKOF AND EXTENDS GEAR FOR COOLING. AT LEVELOFF WITH GEAR EXTENDED; AUTOTHRUST BECOMES DISENGAGED.

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CLBING OUT OF DENVER; OUT OF APPROX 15000 FT; WITH THE CAPT AS PF; WE GOT A BRAKES HOT ECAM. THE CAPT CONTINUED FLYING AND DECIDED TO WAIT AND SEE IF THE TEMP WOULD DECREASE; BUT IT CONTINUED TO INCREASE SLIGHTLY AND DECIDED TO EXTEND THE LNDG GEAR TO COOL THE BRAKES. ATC WAS ADVISED THAT WE WOULD BE SLOWING BUT WOULD CONTINUE OUR CLB TO A CLRED ALT OF FL230. ATC WAS ALSO ADVISED OF THE HOT BRAKE AND THAT WE PLANNED TO EXTEND THE GEAR TO COOL IT AND ISSUED US AN ASSIGNED HDG TO KEEP US CLR OF FASTER TFC. THE CAPT HAD ME ADVISE THE FLT ATTENDANTS AND THEN MADE A PA TO THE PAX BEFORE EXTENDING THE GEAR. THE CAPT HAD ME SET A SELECTED SPD OF 210 KTS SO WE WOULD BE ABLE TO RETRACT THE GEAR AS SOON AS THE BRAKE COOLED. I THEN FOLLOWED THE ECAM; EXTENDED THE GEAR AND WE CONTINUED OUR CLB TO FL230. THE CAPT WAS HAND FLYING; WITH THE AUTOTHROTTLES ENGAGED. WE WERE LEVEL AT FL230 AND AS SOON AS THE ECAM EXTINGUISHED; I ADVISED THE CAPT AND ASKED IF HE WANTED TO LEAVE THE GEAR DOWN A LITTLE LONGER TO COOL MORE BEFORE RETRACTING. ATC WAS ALSO CALLING AT THIS TIME AND THE CAPT STATED THAT HE NEEDED THE GEAR RETRACTED BECAUSE HE WAS UNABLE TO HOLD ALT. I RETRACTED THE GEAR AND NOTICED US DSNDING; SO NOTIFIED ATC THAT WE WERE UNABLE TO HOLD ALT AND WOULD BE BACK AT ALT AS SOON AS THE GEAR WAS RETRACTED. ATC STATED THAT IT WAS NOT A PROB. IT DID NOT MAKE SENSE THAT WE COULD CLB WITH THE GEAR DOWN; THEN BE UNABLE TO HOLD ALT. THAT WAS WHEN I NOTICED THAT THE ENGS WERE AT FLT IDLE AND ADVISED THE CAPT; WHO PROMPTLY DISCONNECTED THE AUTOTHROTTLES AND ADVANCED THE PWR. LOWEST ALT NOTICED WAS FL220 AND WE CLBED RIGHT BACK UP TO FL230 AND CONTINUED THE REST OF THE FLT WITH NO FURTHER PROBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT HE WAS BUSY WITH ECAM PROCS AND THE HOT BRAKES AND DID NOT NOTICE WHAT WAS BEING ANNUNCIATED ON THE FMA. WHEN THE ACFT BEGAN DSNDING HE QUICKLY NOTICED THAT THE ENGS WERE AT IDLE AND INFORMED THE CAPT. AUTOTHRUST WORKED NORMALLY FOR THE REMAINDER OF THE FLT.