I have a paloma tankless water heater, ptg-42pvn. It was flashing, C4, 13 and now it only flashes -0, 13 and will not even turn on. Tried to reset it by unplugging it and it only flashes -0, 13 even when the heater is turned off. Had no issues for over a year and 1/2 and then the last two years have ad the C4, 13 code issue and then today, the display flashes -0, 13..... The all air vents are clean and clear.

http://waterheatertimer.org/How-to-fix-water-heater.html

Delime tankless?
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html#delime

Gene

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

http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html#error
Error codes and troubleshoot on link above
Catch up on maintenance
Hire service technician

Gene

Water Heater Timers Save Money

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

Copy following link for Rheem-Paloma tankless troubleshoot and error codes:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/How-to-install-gas-water-heater.html#install

If unit worked before: Maybe bad PC board. Maybe lack of required yearly maintenance.
Common error codes can be caused by not following maintenance protocol such as cleaning combustion parts, checking gas pressure, checking venting, and air intake, bleeding gas line etc.
Too bad Rheem-Paloma manuals do not show HOW to conduct this maintenance, leaving customer with many unknowns, and no way to oversee that maintenance performed by hired technician is complete, and matches recommended maintenance.
Sell unit on ebay, and install tank-type gas water heater.

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

Copy following link for troubleshoot resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html



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

3" category III stainless for special venting

Tanklessking shows Category III stainless steel vent kit for this model
3" vent
http://tanklessonline.com/rheem-water-heaters-RTG42.html

ptg-42-pvn has minimum 31,000BTU and max 118,000BTU
Max water temperature 120 degrees F
Spec sheet says: 3" special venting
http://www.palomatankless.com/products/42/specifications.html

Hart and cooley show special vent 3" stainless thru-the-wall vent
http://www.hartandcooley.com/specialgasvent/PDF/851515%20Tankless%20Water%20Heater%20Installation%20Vent%20Kits%20sell%20sheet%20-%20HC%20-%20low%20res.pdf

Hot water sources shows thru-wall or thru-roof
http://www.hotwatersource.com/RTG42PVN-Rheem-Indoor-Natural-Gas-Tankless-Water-Heater/RTG42PVN,default,pd.html

http://waterheatertimer.org/pdf/Tankless-roof-vent-installation.pdf

That is good technical question for Rheem.
Open following link for Rheem tankless resources including chat, possible manual, and typical service manual.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

May 2011. If you find exact information from Rheem, then add a comment to this thread so others with same question can find possible answer.

Upvote the help.
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

http://www.palomatankless.com/owners/homeowner+trouble.lasso#28-11
The Controller displays error code "1L."
There is a build-up of lime in your Paloma.
Contact your plumber to service the Paloma by flushing out the lime.
Also search u-tube for flushing lime out of tankless.

I do not have a solution for you, however mine does th same thing. Did you ever find a solution?

increase incoming water pressure

error code 21 is malfunction of air intake filter switch. You need to check and make sure the air filter door is properly seated and that the front panel is properly installed