Water Heaters - Noritz Model N-0751M Error Code 12

First off let me admit that I am new to this forum.
I am a capable guy that has over the years learned to do quite a few home projects including Electrical, Plumbing, and Carpentry. My current work experience is Audio/Video and my past experience was as a master automotive technician for over 25 years, which gives me some experience in mechanical/electronic troubleshooting.

That said, I have recently taken on my home remodel, and one part was to replace an older electric water heater (80 gal) with a new Noritz N-0751M tankless unit . My residence is serviced by natural gas for a dual fuel kitchen range and a "packaged HVAC" unit. My climate is SE Georgia (31546) in USA.

I had stubbed out for the new Noritz unit as an exterior installation, and use 3/4" copper for hot/cold, and 3/4" Black pipe for gas (as recommended in Noritz installation manual. Approximate distance from gas meter to unit is 17 ft. I have run a 110v service with remote cutoff switch, and the Noritz control unit is located in service panel closet of Kitchen. I have no problem with function of range or gas heater.

My issue is that i can get the system to function, but intermittently the Noritz fails to maintain burner operation (red light off, low/no hot water) and eventually the control unit flashes code 12. Based on my checks, it appears that i may have a gas flow/pressure issue which is keeping the burner from staying lit. The Nortiz 751M specifies a gas supply pressure of NG : 4.0" - 10.5" with a (199,900 Btuh) rating.

Is there any static checks (gas meter specifications) or manometer checks that i need to look at. Or is it time to call in a professional?

thanks,

David
:wall:

Without knowing where you tied your gas into I will give you an educated guess. If you tied into an existing line you have to make sure that it has enough capacity to feed your heater and the fixture that it is tied to.

The process of sizing gas is to start at the meter and see what the capacity coming into the house is, you then have to add up all of the btu ratings of all the fixtures, if this figure is more than the meter will deliver you have to have it changed (hope that is not so).

You then start with the most distant fixture btu no. and work toward the meter adding numbers as you go this will give you the size of the next pipe, (you need a gas chart to get these figures) I know a lot of plumbers that don't know how to do this.

If you have a manometer you can check the gas at the heater, if its anywhere near the 4" spec that you cited you probably are not getting enough gas, time for a pro?. :(

I made a home made manometer as per this site:

Using a Homemade Manometer (http://www.leapsecond.com/pages/manometer/)

I first connected the manometer hose end to the gas tap on the side of the gas inlet in heater. I had shut off the gas at the meter as well as my in line cutoff i had installed (3/4"). First I turned on the meter cutoff, and then I slowly opened the 3/4" shut off valve. The water in the manometer shot out of the end of the tubing. For estimate, I'd say I had over 20" of hose above my 0" measurement (static "OFF" level) That should have given me at least a range of 40 WC, correct? (2 X water rise in inches equals WC) I did notice that I have a regulator on outside of my packaged HVAC unit and there is an internal regulator on my dual fuel gas range. Am I in need of a regulator? Or am I barking up wrong tree?

David:wall:

Nogascans: I may have been wrong to suggest that you use a manometer; it could be dangerous without experience.

You have to check the gas at the regulator thats on the fixture. (you do have a regulator on the heater?) The set point should be marked on the regulator body. You have to leave all the other gas fixtures on or you might get a false reading.

28 Inch of water column is aprox. one psi, with the figures you posted that is way too much for your heater, most domestic gas systems run in the 1/2lb. range, (you don't have a 2lb. system in there, do you?).

I still lean toward not enough gas, you didn't tell me where you tied in your 3/4 line, but if you tied it into another 3/4 line theres a good chance that you have over loaded the line, sorry but this is the best I can do from a distance. :(

Shako,

here is what I have. Gas meter is approximately 17 ft (12 ft/tee (to range, HVAC)4 ft from tee to 90 degree (3/4" black pipe), 1 ft up to tankless water heater (the new unit with issue)(3/4" gas pipe) There is no regulator here. This is a new gas run, had electric WH before. This is an exterior unit mounted on outside of house.

I have checked and found a regulator on the HVAC at right before unit (has been there since installed years ago), and gas range has built-in regulator at rear of unit (confirmed).

It appears to me that the gas pressure on the main line is not regulated at meter but was regulated at individual units by the original design.

The Manufacturer (Noritz) specifies a Natural Gas pressure of MIN 4" WC, and MAX 10.5" WC, As mentioned before, there is a gas inlet with a acessable tap for checking with manometer and thats where I got the original measurement.

David

Success!
I installed a Pressure Regulator in the line to the Hot Water heater just below the unit.
I rechecked for leaks, and re-hooked up my homemade manometer to the HW heater service port. With valve open, I had a 5" increase in water height, so I should be right around 10 WC. Started up HW heater and unit is working as advertised.

As a reference, should there be one regulator at service at Gas meter or is it OK (as it was for the range and HVAC) to have individual regulators?

Shako, thanks for the help!

David:thumbup:

Nogascans: It depends on the incomming gas pressure if there is a regulator on the meter, they can be both ways. Since your problem has been worked out with a regulator at your heater and everything else is working you don't need one.

FYI its a good thing that the controls on your heater shut it down, too much pressure will burn out a gas appliance.

Glad its working! Beer 4U2

Me too. Again, thanks for the help!

David