The fact that one hose at the firewall is hot and the other only warm means there is no flow thru the heater core.
Your heat control valve could be bad, it is either on one of those hoses or on the "by-pass" system(4 hoses)
You can try manually opening the valve and see if that other hose heats up, or by-pass everything with some couplers and see if that helps.
Google: Back Flush Heater core
Several videos on how to do this, make and model of vehicle don't matter they are all the same as far as heater core.
Basically you want to push water thru the core backwards(cooler hose to warmer hose) and hopefully push out any debris that may be clogging the smaller core tubes.
Last edited by RonD; 12-30-2014 at 08:55 PM.