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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8767
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a new install from old stock- Tankless Rheem GT-199DV

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I have a new install from old stock- Tankless Rheem GT-199DV and at startup I get error code 13.
It runs 2.5 minutes and then shuts down. I get 6 LED blinks repeating.

I have taken the burner out and checked the flame rods/ igniters and run std service on the Oxygen sensor.

Intake and exhaust are new install and clear.

I still get error 13

Do I have a faulty thermocouple??

Welcome to Just Answer! .

I will stay with you until the situation resolves. I hold questions open after positive ratings to allow for unlimited follow up.

I can look in my files and see if I have the manual on that unit or you can look on the unit sticker for what the 6 blink error code indicates, that will save is some time.

If it is a new installation, and the gas pressure is a little high or low and there will not be proper flame impingement onto the flame sensor rod..... or... the flame will be blowing off of the pilot or main burner heads very slightly... the flame needs to make contact wih the burner heads in order for the SBT flame sensor to work.,, those don't use a standard thermocouple.

It is unlikely the SBT flame sensor is bad on a new unit... it is common for the gas pressure regulator to be set for the wrong pressure and that affects the flame sensing.

Also I need the vent diameter, and details of how the vent is routed and how long the vent run is... I need the same data on the gas line. How long is the run, and what size is it, and what other gas appliances are on the same line.

Meantime I will see if I can find the service manual on that unit.


Customer: replied 4 years ago.


Water line 19 lbs pressure on a 3/4 line. Within listed limits.

Gas line is a dedicated 3/4 line with a 14 foot run from the meter.

I do not know pressure!!!

Vent ID is 4" running 8 foot total vertical with correct outside Noritz termination cap approved by Rheem. Intake is 4" ID and 6 foot run terminatiion.

There are no blockages( paper or packing material) in the runs.

The flame as viewed through the window appears to be pure blue( no white or yellow from oxygen starvation) I cannot tell if it is dancing above the burners.

Nothing on the cover information regarding the LED CB codes.

Customer: replied 4 years ago.

note ---By my found info, the error code 13 is related to oxygen and the sensor..One article mentioned flame rod#2 I cannot find the method to check voltages, resistance.

Hello again,

3/4" pipe used with natural gas, is good for 200,000 btu's for a 14 foot run... but for every 90 degree L or tee, you have to add 5 feet of pipe to the get an equivalent length for sizing the pipe. for instance if you have 5 such fittings you have an equivalent length of 34 feet, thats good for 117,000 btu's of *input.

Your boiler is rated at 199,000 BTU. so input, the 3.4" pipe is generally considered grossly insufficient for the typical gas company pressure regulator settings....the pipe run needs to be 1"'

That said, there is a 50/50 chance that too small gas piping is not the problem... depending on the gas pressure at the utility company meter... if it is a propane rated unit and you are running propane, 3/4" gas pipe at an equivalent length of 34 feet is OK.

I need to know how many fittings are between the gas meter and the water heater.

That said, generally the pressure at a test plug in the burner manifold is 3.5" water column, but I need to confirm that for this model. It may take me a while tomorrow to find the manual on that unit.

meantime let me know how many fittings are in that gas line.

Customer: replied 4 years ago.

Fittings.. only 5 90 degree elbows. One T for the drip leg.


Rheem input fitting is 3/4 and install info also called for 3/4 piping..

Hello again, thanks for the data.

If the run of pipe is 14 feet, and with 5 elblows and one tee (acts as an elbow so we must include it).. thats 6 elbows...5 feet per elblow.. is 30 additional feet..for 44 feet... according to standard practice for piping, that is good for less than 100,000 btu's of heating capacity per the plumbing code for gas appliances..... you have twice that capacity,... and will be suffering low gas pressure at the gas valve in the unit. Look for an 1/8" pipe plug in the gas lines coming to and from the modulating gas valve with all the wires attached. Tell me what you find We can go from there.

That gas line could every easily be the problem about a 90% chance it is at this point..

Did you get an installation manual with the water heater? I am having a hard time finding one.

I am going to bed now, and will back about 8 am tomorrow morning. Let me know if you have the installation manual came with the unit, or if you have a link to it.Thanks! Phil
Customer: replied 4 years ago.

I will search the unit in AM.

Closest thing to a manual is as follows in links Generic models similar models and

showing recommended gas pressures



Hello again

use 0.82" inside pipe diameter for 3/4" pipe.. and 44 feet equivalent get 127 cubic feet of gas per hour.
we use 1,000 btu/cubic foot. (its actually 980 for many natural gasses, some species a bit more some a bit less)

If the gas company regulator is set for 6.5 inches of water column output.. the gas delivery to your gas valve will be too low to put sufficient pressure to the burner heads to operate the burners with enough flame to allow the flame sensors to sense flame properly... so they shut the gas valve off to avoid flooding the room
with unburned fuel.

Your gas flow rate in that will be in the range of 30 to 50% too low. To comply with the building codes the gas line must be sized to 1"... the chances that will solve the problem are 80 to 90% or better... (depends on how the gas company has set the pressure from its meter).

The 3/4" fitting at the gas valve is not larger than that because the orifice inside the gas valve has to be small enough that it modulates well..and that 2" of 3/4" pipe does not restrict the gas flow... all that can be a bit misleading to people not used to hooking these things up.

Customer: replied 4 years ago.

Rheem is trying to tell me my Norits 4" venting on the intake is causing the problem.. telling me to use metal fab crap... I ran error 13 even drawing room air without intake venting.


My gas meter has only 3/4 fittings.. how do I overcome that??

Hello again,

Regarding the gas meter. Call the gas utility and ask them to verify that the gas meter is putting out at least 7 inches of water column pressure and that it is rated for at *least 200 cubic feet per hour gas flow.

If it is, then you can use a 3/4" to 1" bell reducer and run 1" pipe to the water heater. and use another bell reducer there in order to fit the 3/4" gas valve.


Your test without the intake vent connected and still getting the 13 code proves that its not an issue related to the intake vent.

Without seeing and testing the unit and without being able to get the service manual on that unit I cannot verify that your vent piping is correct..

I will opt out of this question, so that other of our experts here can see it and hopefully one of those has the service manual on the unit.

I will keep and eye on the progress, and you can address me again at any time.

Customer: replied 4 years ago.

I'll keep you posted

Thanks, XXXXX XXXXX also be able to see this thread as it progresses and if any of the other experts here have that manual or feel they can help.
Stay in touch as necessary.

Customer: replied 4 years ago.



I did contact my Gas Company ( NIPSCO) and they concur that gas supply is causing the starvation code 13 (not air as Rheem said- but fuel).

You were 100% right. The unfortunate part is I just had the Gas company engineer order a new high volume meter ($300.00). I will then pipe 1 1/4 black independent to the Tankless water heater and am able to T-off that line to supply my stove and furnace at the meter and all will have plenty of volume at the correct pressure. The engineer said that 3/4 would only work within 6 feet of meter and at that its marginal. Thank you again.

Davis Bush

Hello again Davis! Thanks for the feed back!

I will put up the ratings box now so you can rate my answer.... thats how the company pays me from a part of your deposit.

I will hold the question open for you in that case so that you can follow up if needed on the same dime so to speak.


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