- Boilers
- Tankless gas water heater
12
Rinnai 12 on a tankless water heater: flame failure
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
The burner flame was lost or not confirmed. Check that gas is on at the heater and the meter, that a propane tank has gas and that nothing blocks the vent outside. If it repeats, a licensed gas professional must diagnose it.
Safety first
Stop and check this first
- Repeated flame failures can come with incomplete combustion when exhaust recirculates. If code 12 keeps returning, keep the heater off until a licensed professional has checked the vent.
- If you smell gas: do not try to light any appliance, do not touch any electrical switch and do not use any phone in the building. Call your gas supplier from a neighbor's phone and follow its instructions; if you cannot reach it, call the fire department.
Safe checks you can perform
- Gas turned on at the heater and the meter
- Vent outlet outside
- When the code appears
- Propane tank level, if you use propane
- Turn off gas to the heater if it will not operate
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measure inlet pressure and pressure drop
- Do not attempt this professional task: Inspect vent clearances and joint engagement
- Do not attempt this professional task: Check flame rod circuit, grounding and moisture
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Measure inlet pressure and pressure drop
What they doWith a manometer and every gas appliance at the site on high fire, the professional checks inlet pressure against the rating plate and the drop allowed by the gas code Rinnai cites.
They must show youthe readings at rest and with all appliances firing.
In writingwhether the gas system needs resizing.
Inspect vent clearances and joint engagement
What they doThe professional checks terminal clearances, equivalent length, approved materials and that every vent joint is fully engaged.
They must show youphotos of the terminal and joints.
In writingwhat was corrected.
Check flame rod circuit, grounding and moisture
What they doWith power off, the professional checks flame rod and electrode tightness and gap, wiring, the silicone sleeve, ground connections and moisture in harnesses, and isolates components if the code is immediate.
They must show youthe component found faulty.
In writingpart replaced and why.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Gas turned on at the heater and the meter
- Who:
- you.
- How:
- without removing any panel, look at the manual gas valve on the side of the heater and at the valve by the gas meter. Rinnai's owner remedy for 12 is to check that the gas is turned on at the water heater, gas meter or cylinder.
- Result that matters:
- whether a valve was closed.
- If a valve was closed:
- follow Rinnai's operating instructions: power off, valve to OFF, wait five minutes and smell for gas, including near the floor. If there is no smell, turn the valve fully ON, power on and open a hot tap.
- If both valves were already open:
- the gas supply branch is still not ruled out; continue with the next check.
- Evidence to keep:
- photo of each valve position.
Evidence: Rinnai Value Series tankless water heater installation and operation manual
Vent outlet outside
- Who:
- you.
- How:
- from the ground or a window, look at the vent terminal without touching it. Rinnai's owner remedies for code 12 include checking for obstructions in the flue outlet.
- Result that matters:
- whether something visibly blocks the outlet.
- If something blocks it:
- turn the heater off and have a licensed professional clear and inspect the vent.
- If it looks clear:
- recirculation or an internal cause is still possible; continue.
- Evidence to keep:
- photo of the terminal.
Do not climb to the terminal or remove vent parts.
Evidence: Rinnai Value Series tankless water heater installation and operation manual
When the code appears
- Who:
- you.
- How:
- note whether 12 shows immediately when you open a hot tap or after the heater has been running.
- Result that matters:
- the timing of the code.
- If it appears immediately:
- Rinnai's guide points SENSEI models to an electrical short in a component; tell the technician.
- If it appears after running:
- the flame, gas or vent branch is more likely.
- Evidence to keep:
- your notes and the code history.
Evidence: Rinnai USA troubleshooting tankless water heater diagnostic codes
Propane tank level, if you use propane
- Who:
- you.
- How:
- read the tank gauge or ask your propane supplier. Rinnai lists an empty propane tank among the first causes of 12.
- Result that matters:
- whether there is gas in the tank.
- If the tank is empty or very low:
- have it refilled. Rinnai lists bleeding air from gas lines as a licensed professional task, so tell the technician the tank ran out.
- If the tank has gas or you use natural gas:
- continue with the next check.
- Evidence to keep:
- gauge reading and refill date.
Evidence: Rinnai Value Series tankless water heater installation and operation manual
Turn off gas to the heater if it will not operate
- Who:
- you.
- How:
- follow Rinnai's "To turn off gas to appliance": turn off electric power with the On/Off button, set the thermostat to the lowest setting and turn the manual gas valve on the side of the heater clockwise to the full OFF position.
- Result that matters:
- the heater stays off and isolated until a licensed professional or the gas supplier checks it.
- If you smell gas at any point:
- stop and follow the gas warning on this page.
- If you do not smell gas:
- leave it off and call your licensed professional or gas supplier, as Rinnai's operating instructions say.
- Evidence to keep:
- time you turned it off and the last code shown.
Evidence: Rinnai Value Series tankless water heater installation and operation manual
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Rinnai
- Product type
- Tankless gas water heater
Known code variants
- 12
- Ariston Velis 12
- calentador Rinnai 12
- código 12 Rinnai
- Er 12
- error 12 Rinnai
- Rinnai 12
- Rinnai 12 flame failure
- Rinnai code 12
- Rinnai code 12 tankless
- Rinnai error 12
- Velis error 12
What it means
Rinnai lists code 12 as flame failure (No Flame in the Value Series table). Its guide links it to gas supply and inlet pressure, exhaust recirculating because of vent clearance or joint problems, a loose flame rod or electrode, flame rod wiring and sleeve, grounding, moisture in harnesses, debris in the fan and the gas valve. On SENSEI models a code 12 right after water flow begins points to an electrical short. The code alone does not prove the gas valve or board failed.
Warnings and stop conditions
- Higheditorial warning
Repeated flame failures can come with incomplete combustion when exhaust recirculates. If code 12 keeps returning, keep the heater off until a licensed professional has checked the vent.
Evidence: Rinnai USA troubleshooting tankless water heater diagnostic codes
- Criticalsource verified
If you smell gas: do not try to light any appliance, do not touch any electrical switch and do not use any phone in the building. Call your gas supplier from a neighbor's phone and follow its instructions; if you cannot reach it, call the fire department.
Evidence: Rinnai Value Series tankless water heater installation and operation manual
Symptoms and causes
Probable causes · in order
- Gas supply interrupted or lowPossible
Gas off, an empty propane tank, or a gas line or regulator that cannot hold pressure with all appliances firing. Pressure needs a manometer.
Evidence: Rinnai USA troubleshooting tankless water heater diagnostic codes · Rinnai Value Series tankless water heater installation and operation manual
- Exhaust recirculating through the ventPossible
Rinnai says poor terminal clearances or vent joints not fully engaged recirculate combustion gases, causing incomplete combustion and code 12.
Evidence: Rinnai USA troubleshooting tankless water heater diagnostic codes
- Flame sensing circuitPossible
Loose flame rod or electrode, damaged wiring, cracked silicone sleeve or poor grounding. Found by inspection inside the unit.
Evidence: Rinnai USA troubleshooting tankless water heater diagnostic codes
- Electrical short or moisture in connectionsPossible
Distinguished because the code appears immediately after water flow begins, with no flame in the burner box.
Evidence: Rinnai USA troubleshooting tankless water heater diagnostic codes
Virtual technician
Does 12 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Rinnai USA troubleshooting tankless water heater diagnostic codes
Rinnai America · 2024 · manual
- 2
Rinnai Value Series tankless water heater installation and operation manual
Rinnai America · 2019 · manual
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