Tandoor Oven Thermocouple AS12 — Gas Safety Mechanism & Pilot Light Fix for Gas Tandoor Ovens

What Is a Tandoor Thermocouple?

The tandoor oven thermocouple AS12 is the gas safety device — and the most common gas oven thermocouple replacement part — that keeps every Tandoor Morni gas-fired tandoor oven safe to operate. If your gas tandoor pilot light keeps going out, bad thermocouple symptoms are almost always the cause. A thermocouple is the primary gas oven safety component and tandoor safety device — a thin metal sensing element that sits in the pilot flame of the gas burner. Its function: detect the presence of the pilot flame and signal the gas valve to remain open. If the pilot flame goes out for any reason, the thermocouple stops sending its signal and the gas valve closes automatically, cutting off the gas supply. This automatic gas shutoff is the core gas oven safety mechanism — it prevents dangerous gas leaks, gas leak accumulation, and gas leak hazards in any situation where the pilot flame is extinguished unexpectedly. Gas leak prevention is the primary gas safety reason the AS12 thermocouple is fitted to every Tandoor Morni gas oven.

The AS12 is the correct gas tandoor thermocouple replacement — a gas tandoor thermocouple and gas oven thermocouple part for all Tandoor Morni gas tandoor ovens. The tandoor thermocouple works on a simple but reliable physical principle. The AS12 thermocouple is made from two dissimilar metals — a copper and nickel alloy — joined at one end to form a sensing junction. When this junction is heated by the pilot flame, it generates a small thermocouple voltage output (typically 25 to 35 millivolts). This voltage signal — produced by the Seebeck effect — holds the gas safety valve electromagnet open, allowing gas to flow to the main burner. When the pilot flame is extinguished, the sensing junction cools, voltage drops to zero, the electromagnet releases, and the spring-loaded gas valve closes. The entire shutoff process takes approximately 30 to 60 seconds from pilot flame extinction to full gas valve closure.

Bad Thermocouple Symptoms — Signs Your Tandoor Thermocouple Needs Replacing

How to tell if thermocouple is bad: the most common bad thermocouple symptom is the pilot light keeps going out during operation — especially if the pilot won’t stay lit after re-lighting. In a healthy gas tandoor oven, the gas oven pilot light should burn continuously without going out mid-service. Other diagnostic signs:

• Pilot relights but main burner will not stay on — the thermocouple is generating insufficient voltage to hold the gas valve open under the higher gas demand of the main burner.
• Pilot flame goes out within 30 to 60 seconds of lighting — the thermocouple is not warming up sufficiently to generate a holding voltage. Ensure the pilot flame is positioned directly on the thermocouple tip; if it is and the problem persists, replace the thermocouple.
• Visible corrosion or physical damage on the thermocouple wire — the copper sensing wire runs from the gas valve area into the clay chamber. Visible damage indicates replacement is needed immediately.
• Intermittent pilot failures during long service sessions — the thermocouple is degrading under heat stress and losing reliability. Replace proactively before complete failure disrupts service.

Included Free — And Available for Replacement

One tandoor oven thermocouple AS12 is included free in the accessories kit with every Tandoor Morni gas-fired tandoor oven — the Propane Gas Tandoor Oven A02 32×32, Stainless Steel Tandoor Oven A04 34×34, Large Indoor Tandoor Oven A06 36×36, Restaurant Tandoor Oven CH02 32×32, Natural Gas Tandoor Oven CH04 34×34, Middle Eastern Tandoor Oven CH06 36×36, Indian Tandoor Oven T02 32×32, CSA ETL NSF Tandoor Oven T04 34×34, Punjabi Tandoor Oven T06 36×36, Food Truck Tandoor Oven CS02 24×24, and the Portable Catering Tandoor CS03. Tandoor Morni recommends ordering a spare replacement thermocouple at the time of original oven purchase — so a replacement is available immediately when the original fails, without waiting for shipping during a service interruption.

The Thermocouple Safety Circuit

The tandoor thermocouple AS12 is part of a safety circuit that includes three components: the thermocouple itself, the pilot burner assembly, and the gas safety valve. Here is how the circuit operates in normal use:

1. Pilot light is lit manually (or via piezo ignition). The gas valve button is pressed and held, manually holding the gas valve open while the pilot flame lights.
2. Pilot flame heats the thermocouple tip. The sensing junction at the tip begins generating millivolt voltage as it reaches operating temperature — typically 25 to 35 millivolts after 20 to 30 seconds in the pilot flame.
3. Thermocouple voltage holds the gas valve open electromagnetically. Once sufficient voltage is generated, the gas valve solenoid is energised and the valve stays open without manual pressure. The pilot continues to burn, and the main burner can now be ignited.
4. If the pilot flame goes out, the thermocouple tip cools, voltage drops to zero within 30 to 60 seconds, the solenoid de-energises, and the spring-loaded gas valve closes, stopping all gas flow.
5. How to relight the tandoor pilot after a flame failure: press and hold the gas valve button to manually bypass the safety valve, bring a lighter to the pilot assembly, and hold the button until the thermocouple heats and takes over — typically 20 to 30 seconds. If the pilot won’t stay lit after this process, the thermocouple needs replacing.

Why Thermocouples Degrade

The thermocouple sensing tip is continuously exposed to the pilot flame at 800 to 1,000 degrees Celsius. Over time, this continuous heat cycling causes the copper and nickel alloy junction at the sensing tip to oxidise and degrade. As the junction degrades, it generates progressively less voltage — until the voltage output is insufficient to hold the gas valve open under the demand of the main burner gas flow. This degradation is gradual and normal: it is why thermocouples have a defined service life. The only correct response to thermocouple degradation is replacement with a genuine AS12 part.

Thermocouple vs Thermopile — Understanding the Difference

A thermocouple generates a millivolt signal sufficient to power a gas safety valve electromagnet — this is what the AS12 does. A thermopile generates a higher voltage from multiple thermocouple junctions in series and can power electronic ignition control modules. Tandoor Morni gas ovens use a thermocouple (not thermopile) safety system with a standard pilot and piezo or manual ignition. When ordering a replacement, always specify the AS12 thermocouple — not a thermopile, not a generic gas appliance thermocouple. Only the manufacturer-specified AS12 guarantees correct voltage output for the Tandoor Morni gas valve specification.

What a Certified Gas Technician Does During Replacement

A certified gas technician replacing the AS12 thermocouple will: (1) shut off the gas supply and allow the oven to cool completely; (2) locate the thermocouple — a thin copper wire running from the gas valve into the combustion chamber; (3) loosen the thermocouple nut at the gas valve connection and disconnect the sensing tip from its bracket in the combustion chamber; (4) route and connect the new AS12, positioning the sensing tip correctly in the pilot flame path; (5) tighten the nut connection at the gas valve with the mica washer in place; (6) restore gas supply, re-light the pilot, and verify correct operation. The entire replacement process takes 20 to 30 minutes for an experienced gas technician.

Pilot Light Keeps Going Out — Why It Happens & What To Do

When the pilot light keeps going out on a gas tandoor oven, the thermocouple is responsible in the great majority of cases. The thermocouple sensing junction — which sits directly in the pilot flame — degrades over time and generates progressively less voltage. When the thermocouple voltage output falls below 25 millivolts, the gas safety valve cannot hold open against spring pressure and closes automatically. The pilot light won’t stay lit because the thermocouple is no longer generating enough current to signal the gas valve to stay open. The fix: order the AS12 replacement thermocouple (SKU 22578) and have a certified gas technician install it.

How to Tell if a Thermocouple Is Bad — Bad Thermocouple Symptoms & AS12 Diagnosis

How to tell if a thermocouple is bad — three bad thermocouple symptoms to check: (1) pilot light keeps going out — the pilot won’t stay lit after releasing the gas valve button; (2) thermocouple not working fully — the pilot stays lit but the main burner won’t remain on; (3) visible bad thermocouple symptoms — corrosion, soot coating, or physical damage on the wire or sensing tip. Definitive test: use a multimeter. A gas technician connects a multimeter to the thermocouple leads while the sensing tip is heated. A thermocouple multimeter reading below 25 millivolts confirms the thermocouple is bad. Without a multimeter: if the pilot won’t stay lit after 30 seconds of manual button hold, the thermocouple is the most probable fault.

How to Test a Thermocouple — Millivolt Test Procedure

How to test a thermocouple on a gas tandoor oven: a certified gas technician disconnects the thermocouple from the gas valve, heats the sensing tip, and measures thermocouple voltage output with a multimeter set to DC millivolts. Good thermocouple millivolt test result: 25 to 35 millivolts. A thermocouple multimeter reading below 25 mV indicates a bad thermocouple. Thermocouple voltage output below 25 mV cannot be restored by cleaning — replacement is the only remedy. Without equipment: time how long the pilot stays lit after releasing the button. Under 30 seconds indicates thermocouple failure.

How to Clean a Thermocouple — When Cleaning Helps and When It Doesn’t

How to clean a thermocouple on a gas tandoor oven: allow the oven to cool completely, then gently clean the sensing tip with fine emery cloth to remove carbon deposits and soot. How to clean a thermocouple without damaging it: rub gently along the tip axis, not across it, and never bend the sensing junction. Thermocouple cleaning can resolve pilot issues caused by carbon buildup on the sensing tip — but it cannot restore a thermocouple whose internal junction has oxidised. If the pilot light keeps going out even after cleaning, or if the thermocouple multimeter test still shows under 25 millivolts after cleaning, the AS12 replacement thermocouple is needed.

Gas Oven Thermocouple vs Universal Thermocouple — Why Genuine Matters

A gas oven thermocouple replacement must match the exact voltage output specification of the gas safety valve it controls. A universal thermocouple gas oven part may fit physically but generate a different millivolt output than the manufacturer specification — causing the gas valve to behave unreliably. The AS12 is the manufacturer-specified gas oven thermocouple replacement for all Tandoor Morni gas tandoor ovens. Only the genuine AS12 guarantees correct fit, correct voltage, and valid warranty protection.

Tandoor Maintenance — Thermocouple as a Scheduled Spare Part

Proactive tandoor maintenance includes scheduled thermocouple replacement before failure. Good tandoor maintenance practice for commercial kitchens: replace the thermocouple every 18 months as part of a planned tandoor maintenance service visit — regardless of symptoms. This prevents unexpected pilot light failures during service. For restaurants, a complete tandoor maintenance spare parts kit should include: AS12 thermocouple, pilot assembly AS13, and a gas hose AS01. Gas leak prevention and tandoor safety depend on a functional thermocouple — the AS12 is the first-line gas oven safety device and the most important spare part to keep in stock for any commercial gas tandoor kitchen.

How to Relight a Tandoor Pilot & The Seebeck Effect Explained

How to relight the tandoor pilot light correctly: press and hold the gas valve button, bring a lighter to the pilot assembly, and hold the button for 20 to 30 seconds after ignition. This gives the thermocouple time to heat and generate voltage via the Seebeck effect — the physical principle by which two dissimilar metals at different temperatures produce a voltage. The Seebeck effect signal from a healthy thermocouple holds the safety valve open after the button is released. If the pilot won’t stay lit after a 30-second hold, the thermocouple is not generating sufficient Seebeck effect voltage — replace with the AS12.