We have a fast drip coming from the drain, what does that mean?

Probably bad news if steel tank is leaking.

1) Copy following link for do-it-yourself troubleshoot walk-thru:
http://waterheatertimer.org/Leaking-water-heater.html

2) Drain tank and set in a drip pan with drain line to outdoors.
http://waterheatertimer.org/images/Water-heater-drip-pan-2.jpg
http://waterheatertimer.org/Water-heater-will-not-drain.html

3) If tank ruptures, it will flood home

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

If the drip is coming out of drain valve: Put a hose cap over end of drain valve.
If water is seeping out of cracked drain vale, then replace it.
If the leak is seeping around previously sealed threads, then tank may be rusted beyond repair.
http://waterheatertimer.org/How-to-replace-water-heater-drain-valve.html
http://waterheatertimer.org/Leaking-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Before calling Rheem or service technician, open following link for troubleshoot resources including error codes, Rheem chat, typical required maintenance manual, and possible product manual:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf

Error codes are start point for troubleshoot.
Error 14 is 'overheat wrap fault.'
This can include venting problem, failed heat exchanger, bad safety circuit, gas problem.
Rheem does not have a service manual posted for this specific problem.

Additional information: Tankless water heaters consume large amounts of gas during combustion. The combustion burns away hydrogen and the remaining poisonous byproduct is vented into the atmosphere at each home day and night.
Byproduct includes acidic water vapor that condenses along the vent pipe and drips back down vent.
Each tankless vent pipe has a drain line that directs acidic water into household drain.
If this drain line becomes clogged, or if vent was not installed correctly, then water drips down into heat exchanger and can erode or crack exchanger.
The typical maintenance manual above shows steps that can solve many tankless problems before they happen.

Before calling Rheem or service technician, open following link for troubleshoot resources including error codes, Rheem chat, typical required maintenance manual, and possible product manual:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf

Error codes are start point for troubleshoot.
http://waterheatertimer.org/pdf/ErrorcodeTroubleshooting.pdf
Error 14 is 'overheat wrap fault.'
This can include venting problem, failed heat exchanger, bad safety circuit, gas problem.
Rheem does not have a service manual posted for this specific problem.

Additional information: Tankless water heaters consume large amounts of gas during combustion. The combustion burns away hydrogen and the remaining poisonous byproduct is vented into the atmosphere at each home day and night.
Byproduct includes acidic water vapor that condenses along the vent pipe and drips back down vent.
Each tankless vent pipe has a drain line that directs acidic water into household drain.
If this drain line becomes clogged, or if vent was not installed correctly, then water drips down into heat exchanger and can erode or crack exchanger.
The typical maintenance manual above shows steps that can solve many tankless problems before they happen.

make sure that the water is not coming from the over flow tube or the drain valve at the bottem of the tank first. If it is not then yes there is an internal leak and the tank should be replaced

Hello MONON You could try a BOILER DRAIN CAP just screw it on the end of the drain valve to stop the drip.It is brass & avail at any hardware store.

Hello CHUCK The drain can be replaced with a LONG stem brass hose bib.The plastic is a piece of s*#$.They also sell brass drain caps for a easy way out.Just screw it on.

If you mean the safety valve, replace it. They're only a few dollars.

The T&P valve (temperature and pressure) relief valve is suppose to have a 3/4 in drain line threaded into it .This line should have ran to a trapped drain or possibly to the outside of the house. A water heater cannot over fill. To drain your water heater run a garden hose to the outside or to the lowest drain you have nearby.If its still wet be carfull not to get shocked,Attach the garden hose to the drain valve located towards the bottom of the water heater. turn the valve on. If water dosnt come out of the other end of the hose,youll have to see if you can run a peice of wire through the valve into the water heater to get it to drain. This can somtimes be a real problem . I usually leave the water on when i first connect the hose to the drain valve. This allows the water pressure to flush the sedament out of the bottom of the water heater.

If you are refering to the "Dripping coming from the preasure tempature valve,Then just turn off the valve where the water goes into the heater and open the P/T valve with a bucket below it draining only emought water to get below the level where it reaches.     Normally the drain valves are plastic with a Male hosebib attached.  Attach a  garden hose to the rain and run it out to a point lower that the vaslve in order for gravity to drain the tank.The valve opens counter clock wise. If the valve is stuck or does not drain,and you have a foor drain handy,remove the whole valve and replace it with a boiler drain valve.  If The tank is located below the drain level then you will have to either pump or carry the drain water to the higher level.     Replace the P/T valve  and reinstall the associated associated piping. I would use tefelon tape on the P/T pipe theads.    You may have to open a hot water faucet in order for the air to replace the water in the tank ,in order to drain.