A Photograph and a Voltage: Building a Drawing From Nothing

What arrived with the enquiry

Initially an OEM building gas heating appliances needed an ignition and flame-sensing probe. However, what they sent was not an ignition electrode specification.

Instead a photo arrived, plus a wire length and two numbers: 20 kV insulation, 200C heat resistance.

Why those two numbers govern everything

Firstly the 20 kV figure stops the spark finding an easier path than the gap. Certainly high-voltage ignition arcs through weak insulation given the chance. So where it arcs, ignition fails.

Meanwhile the 200C figure is about position. This probe sits close enough to the burner that ordinary cable insulation would harden, crack and fail.

• First, a series of 90 and 140 degree bends, placing the spark gap correctly in the burner.
• Next, a fixed 900mm lead reaching the control module.
• Meanwhile production quantities, so the design had to be manufacturable rather than merely correct.

The part is safety-critical in the plain sense. Namely, if it fails the appliance does not light. Furthermore, depending on the control logic, that can mean unburnt gas.

Deriving the ignition electrode specification

In practice, turning a photo into an ignition electrode specification is most of the work. Meanwhile the material choices turn it into a real specification rather than a sketch.

Why galvanized steel for the probes

Firstly the probes need three things at once. Conductivity, rust resistance and stiffness when hot.

Galvanized steel balances all three. By contrast a softer material lets the probes drift over thermal cycles. The spark gap is the one dimension that must not move.

Why ceramic for the insulator

Ceramic keeps 20 kV in the conductor. Furthermore it survives thousands of heating cycles without cracking.

Together those two properties are why nothing else is used. A polymer insulator meets the voltage and fails on temperature. Meanwhile a lower-grade ceramic survives the heat and eventually tracks.

The dimension that matters most

Notably the bends are not cosmetic. They put the spark gap at a specific point in the burner, where the flame will actually be.

Get that wrong and two things follow. Ignition becomes unreliable. So does flame sensing, since the same probe does both jobs.

What it cost

Nothing unusual, though this project is worth reading as a caution rather than a template.

An ignition electrode specification is only as good as the photo it came from. So we drew it up properly, giving future production a document to build to. Anyone sourcing a safety part this way should insist on the same.

Technical Specifications

Here the insulation voltage and heat resistance rows below are the two the customer gave us. Everything else was derived.

Parameter	Specification
Longwell Part Number	LW-DHZ-02
Component Type	Ignition & Flame Sensor Electrode
Electrode Material	Galvanized Steel
Electrode Diameter	Ø2.5 mm (+0.5/-0)
Insulator Material	Ceramic
Insulator Diameter	Ø11 mm
Wire Length	900 mm
Wire Insulation Voltage	20 kV
Wire Heat Resistance	200°C
Overall Dimensions (Electrode)	Approx. 95 mm x 50 mm

Technical Documentation

The approved drawing sits below. It carries every dimension, material and tolerance the part needs.

LW-DHZ-02.pdf
Here the final engineering drawing details all dimensions, materials, and critical specifications for the LW-DHZ-02 igniter, used by the customer’s design engineers for system integration and by quality control for incoming inspection.

This image provides a clear visual reference of the LW-DHZ-02 assembly, showing the electrode geometry and wire configuration for assembly line technicians and procurement managers.

If you are specifying an igniter

An ignition electrode specification covers a small part that decides whether the appliance works at all.

• Give the temperature at the probe, not in the room. An ignition electrode specification lives or dies on the lead rating. Nearness to the burner sets it. A room-temperature guess fails within a season.
• State the ignition voltage, not the supply. Ignition transformers make tens of kilovolts from a low-voltage input. The insulation must hold the output. So that is the figure to write down.
• Fix the spark gap position dimensionally. Bend angles and lengths place the gap in the flame. So specify them on a drawing rather than in words. A probe in roughly the right place lights roughly reliably.
• Insist on a drawing before production. Photographs and samples suit a first article. A part that must be identical across thousands of appliances needs a document with tolerances, not an interpretation.

See our gas heater blower range, the accessories section, or HVACR components. Appliance safety follows IEC 60335-1.

Questions about electrodes

Why does an igniter lead need 20 kV insulation on a mains appliance?

Because the ignition transformer steps the supply up to tens of kilovolts to jump the spark gap. The lead carries that output, not the mains input. Insulation rated for line voltage breaks down. Then the spark finds a path to earth rather than across the gap.

Can the same probe do ignition and flame sensing?

Yes, and it is common. The electrode sparks to ignite. Afterwards the control module uses flame rectification through the same probe to confirm a flame. Consequently probe position matters twice over, and a displaced gap causes both failures at once.

Why ceramic rather than a high-temperature polymer?

Because the insulator needs dielectric strength and thermal stability together. Polymers rated for the voltage generally cannot hold up at combustion-chamber temperatures over thousands of cycles, and the failure mode is gradual tracking rather than a clean break, which makes it hard to diagnose.

How exact do the bend angles need to be?

Exact enough to be on a drawing with tolerances. The bends set where the spark gap sits relative to the flame, and small deviations show up as intermittent ignition or false flame-loss faults. Those are among the hardest field complaints to trace, which is why the geometry is fixed on paper.