When the igniter glows but nothing lights

This is the fault people argue with us about, and they are right to, because the evidence in front of them appears conclusive. The oven will not light. They open the door, look at the igniter, and see it glowing bright orange. The obvious conclusion is that the igniter is working and something else is wrong.

It is the wrong conclusion, and the reason is worth understanding because it changes how you interpret every symptom that follows.

The igniter is the safety device

On a gas oven, the igniter does two jobs. It lights the gas, and it is also the interlock that decides whether gas is allowed out at all.

The safety valve in the gas line is opened by current. The igniter is wired in series with it, and as the igniter heats, its resistance falls and the current through the circuit rises. When that current reaches the threshold the valve needs, the valve opens, gas arrives, and the igniter — by then extremely hot — lights it. If the current never reaches the threshold, the valve never opens.

That design is deliberate and it is good: gas cannot be released unless something hot enough to light it is already proven to be there.

Why a healthy-looking igniter fails

The consequence of that design is the whole of this article. An igniter ages. Over years of thermal cycling its resistance rises, and rising resistance means falling current. It gets dimmer only slightly. It goes on glowing a convincing orange long after the current it draws has fallen below what the valve requires.

So there is a window — often a long one — where the igniter looks perfect and is functionally dead. During that window the appliance behaves in exactly these ways:

• The oven lights sometimes and not other times.
• It takes much longer to light than it used to, and the owner notices only in retrospect.
• It lights when the oven is cold but not on a second bake when everything is already hot.
• It lights, runs, and then fails to relight when the burner cycles during a long bake, so the oven quietly loses temperature partway through.

Every one of those is normally reported as a thermostat problem, a sensor problem or a board problem. None of them is.

How it is actually tested

With a clamp meter around one leg of the igniter circuit, energised, reading the current it actually draws while it glows. Compare that reading against the specification for the igniter in that appliance. In range or out of range — the question is closed either way in a couple of minutes.

There is a second observation worth making at the same time: how long the igniter glows before gas arrives. A long delay with no ignition at the end of it is the same story told a different way.

Note what is not a test. Colour is not a test. Brightness is not a test. Continuity is not a test either — an igniter with a rising resistance still shows continuity, which is why a meter set to ohms produces a confident and useless result.

What follows from a bad reading

Replacement, and one piece of handling advice: these elements are brittle and their useful life is shortened by being touched. Handle a new one by its bracket and its leads.

If the reading is in range, the igniter has been ruled out with a number rather than a glance, and the survey moves on to the gas supply and the safety valve itself before anything electronic is considered.

Why this one gets its own entry

Because the igniter is a consumable and the board is not. On the equipment we see around Fleming Island, an igniter reaching the end of its life is one of the two or three most common reasons a professional range or wall oven stops working, and it is routinely misdiagnosed as something four or five times the price. Checking it takes a few minutes and it comes early in the survey for exactly that reason.