How a tankless water heater lights: ignition codes by brand

You open a hot tap, the water stays cold, and the display shows a code such as E003 (Navien), 11 (Rinnai, Rheem, Noritz) or A011 (Rheem IKONIC). Each is that brand’s code for a failed ignition, but the manufacturers describe what the heater does before it shows the code in different depth. This page sets out what their own documents say, series by series, with the page for each point.

What the manuals say happens when you open a tap

All four brands tie the start of the heater to water flow and print the flow it needs:

Brand and series	Flow to start heating
Navien NPE-2 and NPN (Navien NPE-2 Installation Manual, p. 7; Navien NPN Installation Manual, p. 7)	0.5 GPM (1.9 L/min) minimum flow rate
Rinnai SENSEI RU (Rinnai 100000467, p. 12)	0.4 GPM (1.5 L/min) minimum activation flow, which “may vary slightly depending on the temperature setting and the inlet water temperature”
Rheem RTGH-3 and RTG-3 (Rheem AP21822, pp. 10, 12)	0.4 GPM to start; 0.26 GPM “Extinction Flow Rate”
Rheem IKONIC (Rheem AP23209, p. 37)	0.4 GPM to activate
Rheem ThermaForce (Rheem 84160404, pdf p. 3)	0.5 GPM (1.9 L/min)
Noritz EZ and NRCR (Noritz SBB81M1, p. 29)	0.4 GPM (1.5 L/min) to start; 0.26 GPM (1.0 L/min) to keep heating
Noritz NRCP (Noritz NRCP111 Owner’s Guide, p. 35)	The unit starts when the inlet water flow sensor “detects flow over 0.5 gpm”

After that point the documents differ. Rheem’s ThermaForce manual is the only one we read that prints a sequence of operation. For Rheem’s other tankless series and for Rinnai, the steps turn up one at a time in troubleshooting text. For Navien and Noritz, the sequence is not described in the documents we read. Both brands’ service manuals open only after you accept terms on the manufacturer’s site, and we did not read them.

Rheem ThermaForce (RTGH-L199i): the printed sequence

The ThermaForce installation manual has a Sequence of Operation section, and the controller manual repeats it (Rheem 84160404, p. 2-5; Rheem 84162404, p. 1-38). The first five steps, as printed:

1. “The unit receives a call for […] domestic hot water heating from the internal flow sensor.”
2. “The unit performs a safety check and energizes the fan for a pre-purge (Service Display = 3).”
3. “Once the 5-second pre-purge is complete, the unit enters a 5-second trial for ignition (Service Display = 4).”
4. “Once the burner is lit and flame has been proven the unit operates as it is programmed […]”
5. “If the unit exceeds its target temperature and there is still a call for hot water the burner will turn off. (Service Display = 1)”

Step 3 goes on: “If the unit fails to ignite, the unit will complete another 5-second pre-purge then 5-second trial for ignition. This is repeated 4 times before a hard lock-out occurs.” To start again, “The Return button […] must be pressed to reset the controller and begin another trial for ignition” (Rheem 84160404, p. 2-5). The fault table words the code, F004, as “No flame detected during four ignition trials” (Rheem 84160404, p. 5-5). The manual does not reconcile “repeated 4 times” with “four ignition trials”, so we do not add up a total.

The service display shows the stage: 3 is “Fan Pre-purge and Post-purge” and 4 is “Trial for Ignition and Flame Proving” (Rheem 84160404, p. 2-5). These steps and times belong to the ThermaForce (also sold as the Ruud L-Series). Its codes are F numbers, F004 and F005, not the 11 and 12 of Rheem’s other tankless lines (Rheem 84160404, pp. 5-5, 5-6).

Rheem RTGH-3, RTG-3, RTG-R-3 and IKONIC: pieces from the code explanations

Rheem’s technician manuals for these series (AP21822 for RTGH-3 and RTG-3, AP24838 for RTG-R-3, AP23209 for IKONIC) and the owner manuals have no sequence-of-operation section and give no time for a purge or an ignition attempt. Their code explanations do mention the steps. We list them in the order of the steps they name; the manuals do not number them, and they do not say whether the pre-purge or the no-flame check at the rod comes first.

• Water flow starts it. For one check the technician is told to “turn on water flow to begin ignition sequence” (Rheem AP21822, p. 55).
• A pre-purge comes before ignition. The vent codes read: “90 - Error Code will occur BEFORE unit goes into ignition. 99 - Error Code will occur AFTER unit shuts down.” Both are for blockage found “during the pre-purge OR post-purge cycles” (Rheem AP21822, p. 61).
• The flame rod must see no flame before the igniter fires. If it does, the heater shows 72 (Rheem AP21822, p. 55).
• The igniter rod and coil make a spark that shows through the sight glass. The code 11 check sends the technician to them “If the spark is NOT visible through the sight glass”, and to the flame rod when the spark is visible (Rheem AP21822, pp. 38–39).
• The flame rod then has to detect flame: “In the case of ignition failure, the water heater will attempt ignition 2 times. If no flame is detected, the water heater displays the “11” error code” (Rheem AP21822, p. 37; Rheem AP24838, p. 30). The manual does not say whether the 2 times include the first try.
• If the flame goes out while the burner runs, the heater “stops supplying fuel, attempts to restart, counts the incidents of flame loss”, and shows 12 when that happens 3 times in a row (Rheem AP21822, p. 40; Rheem AP24838, p. 33).
• Once the heater is off, the flame rod should stop seeing flame. Flame still detected “a few seconds after turning the water heater off” gives code 52, which the manual files under the proportional gas valve (Rheem AP21822, p. 50).
• After the tap closes, the fan keeps turning: “Fan continues to rotate after the hot water faucet is closed. The post-purge cycle clears flue gases. Normal operation.” (Rheem AP21820, p. 73; Rheem AP22745, p. 105).

The IKONIC service manual counts differently. A011 comes after the heater will “attempt ignition 10 times (Including the post purge every 3 times)”, and A012 after flame loss “occurs 15 times consecutively” (Rheem AP23209, pp. 38, 41). IKONIC is the only Rheem series whose manual puts a post-purge between ignition attempts.

Rinnai: an “ignition cycle” and a bulletin diagram

Rinnai’s installation manuals and its service document, Troubleshooting Tankless Water Heater Diagnostic Codes (100000652), have no sequence-of-operation section. When water runs and nothing happens, with no code, the service document checks the minimum activation flow and whether “the water flow turbine spins freely” (Rinnai 100000652, p. 69).

The same document refers to an “ignition cycle” that water flow starts. Its spark test for code 11 says to “initiate hot water flow to initiate ignition cycle” and look for a spark (Rinnai 100000652, p. 16). On SENSEI models the spark electrode voltage is measured “during ignition cycle” (Rinnai 100000652, p. 16); for non-SENSEI models, “there will be no voltage present unless the water heater is going through the ignition cycle” (Rinnai 100000652, p. 18). Once there is flame: “If you see a flame in the burner box while the water heater is cycling, the water heater should continue to operate. If the flame goes out, there is an issue with the flame rectification circuit or gas system.” (Rinnai 100000652, p. 16).

Rinnai draws the sequence in one place: Technical Bulletin TB-166, Updates to PC Board Ignition Sequence (12/2019). Its text: “Currently, there are three ignition attempts on SENSEI and I-Series products before the unit displays a Code 11 (SENSEI) or a Code 110 (I-Series).” The software was updated “to increase the number of ignition attempts to 18”, and the bulletin gives the reason: “This software update will improve ignition performance by increasing the number of attempts to purge residual air that may exist in the gas line.” (Rinnai TB-166, p. 1).

The bulletin’s diagram compares the two sequences (shown on the diagram; this is our reading of the page image, since most of its labels exist only as an image). In the old sequence a prepurge check comes first, then three numbered attempts, with the label “Gas valve open” above the first, then code 11. The new sequence starts the same way. After attempt 3 the diagram shows a forced exhaust and another prepurge check before attempts 4 to 6, skips ahead, and shows the same pair before attempts 16 to 18, then code 11. It has no time scale and marks neither the spark nor the flame (Rinnai TB-166, p. 1).

The bulletin names SENSEI and I-Series products only; I-Series products, which show code 110, are boilers and are outside this page. It does not name the SENSEI RX/CX models, which Rinnai’s 2024 service document lists as a separate group, or the non-SENSEI RE, REP and V series (Rinnai 100000652, p. 16). It does not say which software version or serial numbers have 18 attempts.

Navien: parts and a flow figure

Navien’s NPE-2 and NPN user’s, installation and remote controller manuals describe no ignition sequence and never use the word spark. The NPE-2 component diagram names the parts involved, among them the “Ignition Transformer”, “Igniter/Flame Rod”, “Flow Sensor”, “Fan Motor”, “Air Pressure Sensor (APS)” and “Gas Valve” (Navien NPE-2 Installation Manual, p. 9). The specification table lists “Electronic Ignition”, with the flame rod among the safety devices (Navien NPE-2 Installation Manual, p. 7). In the NPE-2 User’s Manual the fan and the air pressure check come up, beyond the parts lists, only as causes of codes E109 and E110 (Navien NPE-2 User’s Manual, p. 17). The installation manual also lists “Current RPM” (“Fan RPM”) and “Current APS” (“APS voltage”) among the installer’s service status items, with no step that uses them (Navien NPE-2 Installation Manual, p. 95).

For an owner, Navien’s troubleshooting chart asks whether the hot water faucet is open wide enough to draw “at least 0.5 gallons of water per minute (GPM) through the water heater” (Navien NPE-2 User’s Manual, p. 16). Navien’s FAQ page for the NPE-A2 says that with no hot water and no error code, “The issue is most likely the flow sensor inside the unit is not spinning properly”, and recommends contacting the original installer or a Navien Service Specialist (Navien NPE-A2 FAQs page).

The installer’s gas pressure test shows one more piece of behavior. With a hot tap open, “The water heater should turn on and the gas in the gas supply line will be purged”; with the manual gas valve shut, the installer leaves the faucet on “until the water heater shuts down due to a lack of gas supply” (Navien NPE-2 Installation Manual, pp. 24, 25).

The installer menu counts “2nd Ignition”, “3rd Ignition”, “4th Ignition” and “5 - 10th Ignition” events (Navien NPE-2 Installation Manual, p. 99). No Navien manual we read says how many attempts come before E003.

Noritz: flow, an attempt count on NRCP, no sequence

The Noritz owner’s guides, installation manuals and technical data sheets we read have no sequence-of-operation section and do not use the words pre-purge or post-purge. The EZ installation manual says: “This water heater does not have a pilot light. It is equipped with an ignition device that automatically lights the burner. Do not attempt to light the burner by hand.” (Noritz SBB81M3-1, p. 61). The NRCP specification lists “Direct Electronic Ignition / Automatic Flame Sensing” (Noritz NRCP111 Installation Manual, p. 6). Its technical data sheet shows the flame sensor checked before the gas valve opens, with code “Er72 Flame detected before gas valve opens” and a sensor reading of “5 VDC when flame is off” (Noritz NRCP111 Technical Data Sheet, p. 2).

The EZ owner’s guide separates two failures an owner can see. “The water heater does not attempt to ignite when water is running” points to reversed plumbing, crossed pipes or the water filter. “The water heater attempts to ignite but fails” points to a reset, possible air in the gas line and a professional check of the gas supply pressure (Noritz SBB81M1, p. 28).

On NRCP models the blower keeps going after the burner stops: “The blower operates for three minutes after combustion has stopped to purge remaining exhaust gas from the flue.” (Noritz NRCP111 Owner’s Guide, p. 35). The NRCP guides are also the only Noritz documents with an attempt count, printed in the code row itself: “Er:11 Ignition has failed 10 (Ten) times” (Noritz NRCP111 Owner’s Guide, p. 34). The NRCP1112 and NRCP982 guide prints the same row (Noritz NRCP1112 Owner’s Guide, p. 39). The EZ, EZTR40 and NRC98 guides give no count.

On first start, the EZ installation manual tells the installer that with code 11 “air may be trapped in the gas line”. The routine: close the hot fixture, turn the heater off and back on, reopen the fixture, and “If necessary, repeat until the air is completely purged from the gas line.” (Noritz SBB81M3-1, p. 60).

1. Call for domestic hot water heating from the internal flow sensor

2. Safety check

3. 1. Fan pre-purge, 5 s Service display 3

   2. Trial for ignition, 5 s Service display 4

   Fails to ignite: repeated 4 times

   1. Hard lock-out

   2. Press Return to reset the controller

4. Flame proven

5. Unit operates as programmed

6. Target temperature exceeded, call still on: burner off Service display 1

Fault table, p. 5-5: F004 “No flame detected during four ignition trials”. The manual does not say that F004 is the hard lock-out.

1. Water flow begins ignition sequence

2. Order not stated

   Pre-purge

   Vent blockage before ignition: code 90

   Flame rod must read no flame

   Otherwise: code 72

3. Igniter rod spark, visible through the sight glass

4. Flame rod detects flame

   No flame after “attempt ignition 2 times”: code 11

5. Tap closed

6. Fan post-purge

   Vent blockage after shutdown: code 99

Previous: 3 ignition attempts

1. Prepurge check

2. Gas valve open

   Attempts 1 2 3

3. Code 11

New: 18 ignition attempts

1. Prepurge check

2. Gas valve open

   Attempts 1 2 3

3. Forced exhaust

4. Prepurge check

5. Attempts 4 5 6

6. Break in the line, as drawn; attempts 7 to 15 are not drawn

7. Forced exhaust

8. Prepurge check

9. Attempts 16 17 18

10. Code 11

Numbered squares are ignition attempts. The bulletin draws no time scale and marks neither the spark nor the flame.

Ignition code by brand

The numbers 11 and 12 recur across brands, but the names and the conditions behind them differ. Rinnai’s 11 is “No Ignition (Heater Not Turning On)”; Rheem’s 11 follows “attempt ignition 2 times” with no flame detected; Noritz NRCP’s Er:11 is “Ignition has failed 10 (Ten) times”. Read the row for your series. “Not stated” means the documents listed for that row do not give it.

Brand and series	No-ignition code	Flame-loss code	Attempts before the code	Reset	Who
Navien NPE-A2/S2 (Navien NPE-2 User’s Manual, pp. 10, 16, 17; Navien NPE-2 Installation Manual, p. 99; Navien NR-21DU, p. 26)	E003 “Ignition failure”	E012 “Flame loss”	Not stated; the installer menu counts 2nd to 10th ignitions	Back button; on the NR-21DU remote, OK, then “RST” shows	Owner: gas valve and reset; then an authorized technician, a licensed professional or Navien Technical Support
Navien NPN (Navien NPN User’s Manual, pp. 12, 21, 22)	E003 “Ignition failure”	E012 “Flame loss”	Not stated	Reset button; outdoor models: OK, then “RST” shows	Same as NPE
Rinnai SENSEI RU (Rinnai 100000467, p. 73; Rinnai TB-166, p. 1)	11 “No Ignition (Heater Not Turning On)”	12 “No Flame”	3 before a software update, 18 after	None printed for 11 or 12	Owner first; “Some of the checks below should be performed by a trained and qualified professional”
Rinnai SENSEI RX/CX (Rinnai 100000849, p. 1; Rinnai 100000652, p. 3)	11 “No Ignition (Heater Not Turning On)”	12 “No Flame”	Not stated; TB-166 does not name RX/CX	None printed for 11 or 12	Owner first; the service document is for trained and qualified professionals
Rinnai RE (Rinnai 100000722, pp. 49, 50; Rinnai 100000652, p. 3)	11 “No Ignition (Heater Not Turning On)”	12 “No Flame”	Not stated; TB-166 does not name non-SENSEI series	None printed for 11 or 12	Owner first; the service document is for trained and qualified professionals
Rheem RTGH-3, RTG-3 and RTG-R-3 (Rheem AP21822, pp. 7, 37, 40; Rheem AP24838, pp. 30, 33; Rheem AP21820, pp. 74, 75)	11 “Flame Not Detected by Flame Rod”	12 “Detected Presence of Flame, Then Lost it”	11: “attempt ignition 2 times”; 12: flame lost 3 times in a row	RTGH-3 owner manual: POWER off, wait about 5 minutes, on; if the code stays, unplug for about 30 seconds	Owner (RTGH-3 owner manual): gas valve and reset; the troubleshooting manual is for “technicians and service professionals ONLY”
Rheem IKONIC S/SR (Rheem AP23209, pp. 5, 38, 41; Rheem AP22745, p. 106)	A011 “Flame Not Detected From Flame Rod”	A012 “Unit Detected Flame and Lost It”	A011: 10, “Including the post purge every 3 times”; A012: 15 flame losses in a row	SERVICE, ENTER, then “Clear Alarms?” and “Yes”	Owner clears the code; the service manual is “only intended for qualified service technicians”
Rheem ThermaForce RTGH-L199i (Rheem 84160404, pp. 2-5, 5-5, 5-6)	F004 “No flame detected during four ignition trials”	F005 “No flame detected during operation”	5-second pre-purge and 5-second trial, “repeated 4 times before a hard lock-out”	Return button after a hard lock-out; fault codes: touch the wrench for 2 seconds	Not stated
Noritz EZ and NRCR (Noritz SBB81M1, pp. 28, 31; Noritz SBB81M3-1, p. 61)	11 “Ignition failure”	121, 122 “Flame loss”, in the installation manual only	Not stated	Close and reopen the hot fixture, or turn the power off and on	Owner: gas valve and reset; “Have a professional check the gas supply pressure”
Noritz EZTR40 and NRC98 (Noritz SBB809K-2, p. 24; Noritz SBB80JP-3, p. 28)	11 “Ignition error”	Not in the owner’s guide	Not stated	Turn the unit off, open a hot fixture, turn it back on	Owner steps only; the row names no professional
Noritz NRCP111, NRCP98, NRCP1112, NRCP982 (Noritz NRCP111 Owner’s Guide, p. 34; Noritz NRCP1112 Owner’s Guide, p. 39; Noritz NRCP111 Technical Data Sheet, p. 2)	Er:11 “Ignition has failed 10 (Ten) times”	Er12 “Flame Loss”, in the technical data sheet only	10	Power button; Er:11 is a hard lockout, cleared by turning the power off and then on	“Contact the installer or Noritz America Technical Support” if it happens again

Rinnai prints no reset step for codes 11 and 12 in the documents we read. Its reset instructions are for other codes; for code 03 the service document says “Press ON/OFF button on controller twice; this resets the diagnostic code.” (Rinnai 100000652, p. 9).

The checklists for these codes go beyond the gas supply. Rinnai’s code 11 row also lists the PC board ground wire, the flame rod wire, the igniter, the gas solenoid valves, the gas orifice and the condensate line (Rinnai 100000467, p. 73). Navien’s NPN row adds a check that “the gas manifold and the fuel DIP SW setting match the supplied gas type” (Navien NPN User’s Manual, p. 22). And on a Noritz EZ, code 11 can appear during a manual drain with the gas valve closed; the owner’s guide says: “This is not a malfunction of the water heater.” (Noritz SBB81M1, p. 25).

What an owner can check

Every owner’s table in this set lists a gas valve check for the no-ignition code. Navien, Rheem and Noritz also print a reset; Rinnai prints none for codes 11 and 12. These steps stay outside the heater’s cover:

1. Open the hot tap fully. Rheem’s owner chart: “Open hot water faucet completely. (The main burner goes off when incoming water volume is inadequate.)” (Rheem AP21820, p. 72). The flow each brand needs is in the first table on this page.
2. Check that the gas valve to the heater is open. Navien: “Ensure that the main gas supply valve is open.” (Navien NPE-2 User’s Manual, p. 17). Rheem: “Check shut-off valve and open completely.” (Rheem AP21820, p. 75). Noritz: “Check whether the gas valve is open.” (Noritz SBB81M1, p. 31). Rinnai asks you to check that the gas is on “at the water heater, meter, or cylinder” (Rinnai 100000467, p. 73).
3. On propane, check the tank. Rinnai: “If the system is propane, make sure that gas is in the tank.” (Rinnai 100000467, p. 73). Rheem’s owner row for code 12 lists “LP gas is running low (LP models only).” (Rheem AP21820, p. 75).
4. Reset the heater as the table above gives for your series, then open a hot tap and watch the display. For Rinnai 11 and 12 there is no printed reset.
5. If the code comes back, stop and call. Rheem: “Make note of the displayed error code and call for service assistance.” (Rheem AP21820, p. 74). Navien: contact “an authorized technician, a licensed professional, or Technical Support” (Navien NPE-2 User’s Manual, p. 16). Noritz NRCP: “Contact the installer or Noritz America Technical Support for assistance.” (Noritz NRCP111 Owner’s Guide, p. 34).

If nothing happens at all when you open a tap and no code appears, the manuals treat it as a separate case. Rinnai’s row “NO CODE - Nothing happens when water flow is activated” lists the minimum flow rate, the inlet water supply filter and, on new installations, hot and cold lines that may be reversed (Rinnai 100000467, p. 75). Noritz lists reversed plumbing or crossed pipes and the water filter (Noritz SBB81M1, p. 28).

For the flame-loss codes, Navien’s NPE-2 table says “Clean the intake air filter.” (Navien NPE-2 User’s Manual, p. 17). Rheem’s owner row for 12 reads “Gas service has been interrupted. Contact your gas utility company.” (Rheem AP21820, p. 75). For the no-ignition code, the IKONIC owner row for A011 adds a check that “venting/air supply is not blocked” (Rheem AP22745, p. 107).

A fan that keeps running after you close the tap is normal by Rheem’s charts (Rheem AP21820, p. 73). On a Noritz NRCP it runs for three minutes (Noritz NRCP111 Owner’s Guide, p. 35).

What is technician work

The documents hand the gas side and the ignition parts to professionals. Navien: “Measuring the inlet gas pressure should be performed by a licensed professional only.” (Navien NPE-2 Installation Manual, p. 24). Rinnai’s service document: “Only trained and qualified professionals are permitted to follow the instructions in this document.” (Rinnai 100000652, p. 3). Its code 12 section opens with “You must be qualified to service gas systems before proceeding” (Rinnai 100000652, p. 20). Rheem’s owner manual: “For Your Safety, DO NOT attempt repair of electrical wiring, gas piping, remote control, burners, vent connectors, or other safety devices. Refer repairs to a qualified service technician.” (Rheem AP21820, p. 74). Noritz makes the gas system “the sole responsibility of the installer” (Noritz SBB81M3-1, p. 36). Rheem’s technician manual warns: “The ignition cable carries more than 10,000 volts of electrical energy.” (Rheem AP21822, p. 7).

Rinnai’s owner table for code 11 lists some of these items too, such as gas type and inlet pressure, bleeding air from the gas lines, the igniter and the gas solenoid valves. Above the table it says “Some of the checks below should be performed by a trained and qualified professional”, without marking which (Rinnai 100000467, p. 73). Treat the gas and ignition items as a technician’s job.

For the no-ignition code, the technician documents check these points:

• Rheem RTGH-3 and RTG-3, code 11: gas pressure at the heater’s gas connection, both static (“Gas pressure during standby”) and dynamic (“Gas pressure at max combustion”), because “the use of another gas appliance may cause a possible drop” (Rheem AP21822, p. 37). Then the igniter rod and coil, or the flame rod, depending on whether the spark shows (Rheem AP21822, pp. 38–39).
• Rinnai SENSEI and SENSEI RX/CX, code 11: inlet pressure against the rating plate, held with “all gas water heaters at the location firing on high fire”; a spark test with the igniter wire unplugged and held “about a 1/4 in. from a metal item on the water heater”; a spark electrode gap of “0.138 in. or 3.5 mm”; and the flame rod, for “a buildup of carbon or a white substance” among other faults (Rinnai 100000652, p. 16). If something inside the gas valve “may be preventing the gas valve from occasionally opening”, the step is “Replace gas valve.” If inlet pressure drops below the allowable value: “Have the gas system checked by a professional gas technician that specializes in gas system sizing and troubleshooting.” (Rinnai 100000652, p. 17). The RX/CX tech sheet gives “1 μ amp or greater for proper flame circuit” (Rinnai 100000849, p. 1).
• Noritz NRCP, Er11: “Make sure that the gas supply and inlet gas is within specification. Check spark from the burner window.” (Noritz NRCP111 Technical Data Sheet, p. 2).
• Rheem ThermaForce, F004: verify that the external gas shutoff valve is open and that gas inlet pressure is at least 4 in. w.c. during the ignition trial (Rheem 84160404, p. 5-5).

Inlet gas pressure, for the technician

These ranges are reference for whoever connects a manometer to the gas line. They differ by series and document, so there is no single standard range. Rinnai’s service document sends the technician to the rating plate on the side of the heater (Rinnai 100000652, p. 16).

Brand and series	Natural gas	Propane
Navien NPE-A2/S2 and NPN (Navien NPE-2 Installation Manual, p. 24; Navien NPN Installation Manual, p. 23)	3.5–10.5 in. WC	8.0–13 in. WC
Rinnai SENSEI RU (Rinnai 100000467, p. 12)	3.5–10.5 in. WC	8.0–13.5 in. WC
Rinnai SENSEI RX (Rinnai 100000883, p. 2)	3.5–10.5 in. WC	8.0–13.5 in. WC
Rinnai RE (Rinnai 100000722, p. 10)	4.0–10.5 in. WC	8.0–13.0 in. WC
Rheem RTGH-3 and RTG-3 (Rheem AP21822, p. 37)	4.0–10.5 in. WC	8.0–13.0 in. WC
Rheem IKONIC (Rheem AP23209, p. 38)	4.0–10.5 in. WC	8.0–13.0 in. WC
Rheem ThermaForce (Rheem 84160404, pdf p. 3)	4–14 in. WC	4–14 in. WC
Noritz EZ, Rev. 10/25 (Noritz SBB81M3-1, p. 38)	3.5–10.5 in. WC	8–13 in. WC
Noritz NRCP111 and NRCP98 (Noritz NRCP111 Installation Manual, p. 6)	3.5–10.5 in. WC	8.0–14 in. WC
Noritz EZTR40 (Noritz SBB809L-2, p. 16)	4–10.5 in. WC	8–14 in. WC

Some documents add their own limits. Rinnai’s service document says inlet pressure “should never exceed 10 inches water column for natural gas or 13.5 inches for propane” (Rinnai 100000652, p. 17), below the 10.5 in. maximum in its manuals. The SENSEI RX manual asks that, after installation, pressure at each gas appliance not drop below 5.0 in. w.c. (1.2 kPa) for natural gas or 8.0 in. w.c. (2.0 kPa) for propane “while all gas appliances operate at the maximum input rate” (Rinnai 100000839, p. 44). The Noritz EZTR40 manual requires at least 5 in. WC for natural gas and 8 in. WC for propane for all appliances in the gas system, above its 4 in. table minimum for natural gas (Noritz SBB809L-2, p. 16). Noritz also states what low pressure does: “Gas pressures below the required minimum pressure may result in ignition failure, personal injury, or loss of life.” (Noritz SBB81M3-1, p. 38).

Ignition and flame-loss codes on this site

• Navien: E003, ignition failure; E012, flame loss; all Navien tankless codes
• Rinnai: 11, no ignition; 12, no flame; all Rinnai tankless codes
• Rheem: 11, flame not detected; 12, flame detected and then lost; all Rheem tankless codes
• Noritz: 11, ignition failure; all Noritz tankless codes

What these documents do not cover

• We did not read the Navien and Noritz service manuals, which open only after you accept terms on the manufacturer’s site. The sequence and the attempt count for those brands may be there.
• Only the ThermaForce manual (5-second pre-purge, 5-second trial) and the Noritz NRCP guide (three minutes of blower after combustion) print any times. The other documents give none.
• None of the documents describes how the burner varies its output. They name a “Modulating gas valve” (Navien NPN User’s Manual, p. 22), a proportional gas valve (Rheem AP21822, p. 50) and an “Air ratio valve” (Noritz NRCP111 Installation Manual, p. 6) and stop there.
• Rinnai mentions a “flame rectification circuit” and gives a microamp figure, but no brand explains how a flame rod senses flame.
• Each quote belongs to the series and revision named with it. Several documents are years old (the Navien NPE-2 User’s Manual is from 2020, the Noritz EZTR40 and NRC98 guides from 2017), and Rheem’s troubleshooting and use and care manuals print no issue date. Check the manual for your own model.

See also

• Water heater size calculator
• 2029 water heater regulations: the DOE standard from May 6, 2029
• Furnace and HVAC tax credits for 2025 and 2026: 25C ended after 2025
• Form 5695 for 2025 and 2026: QMID, lines, carryforward
• Home maintenance schedule from the manuals: monthly to yearly
• Winter home maintenance checklist: furnace, boiler, water heater
• Water heater or furnace closet: clearance and air requirements

Error codes: Navien, Noritz, Rheem, Rinnai