Hot spot on the coil - rectify uneven annealing

A hotspot is a point within a wire winding that becomes hotter than the rest of the coil when fired. Normally, the current should flow evenly through all the windings, so that the coil heats up from the inside out – in a controlled and uniform manner. With a hotspot, the heat concentrates on a single winding or at a contact point between two windings.

The reason lies in physics: if two windings touch, a short circuit occurs at that point. The current takes the path of least resistance, individual sections of wire are bypassed, and the energy is distributed unevenly. The result: the coil heats up unevenly, usually first at the outer coils, whilst the centre remains dark – or vice versa. A coil hotspot practically only occurs with self-wound coils, i.e. in RDA, RTA or RDTA atomisers. Pre-made mesh coils and glued-in head coils are not usually affected by this.

A coil hot spot can have several causes. In practice, three scenarios are particularly common.

Windings touch each other

In contact coils, the windings are deliberately placed against each other, whereas in spaced coils they are separated. If the coil slips during installation or when threading the cotton, individual rings may overlap or become misaligned. This is where the classic short-circuit hotspot occurs.

Wire quality and alloy

Low-quality Kanthal or nickel-chromium wires often have inconsistent cross-sections. Even small variations in diameter mean that thinner sections glow faster. Kinks in the wire during winding also create weak points where heat concentrates.

Poor contact at the terminals

If the wire ends are not securely and cleanly screwed into the base’s terminals, the contact resistance increases. The coil receives less energy, whilst individual areas heat up more intensely. Oxidised terminal contacts further exacerbate this effect.

Fixing a hotspot isn’t rocket science, but it does require care. Only work on a safe mod with short-circuit protection or on a dedicated ohmmeter. Go through these points in order:

• Remove cotton wool: Always check for and fix hotspots on a dry, empty coil. Cotton wool in the coil will burn immediately if you fire it for too long.
• Pulse, don’t hold: Press the fire button in short bursts of one second each at low power (approx. 15–25 watts depending on coil resistance). This allows you to see where the coil is glowing unevenly without damaging the wire.
• Use ceramic tweezers: Using heat-resistant tweezers, gently squeeze and pull the coils together whilst the coil is glowing. Never use metal tweezers – this causes a direct short circuit to the deck.
• Work from the inside out: A properly glowing coil starts to light up in the centre and spreads the heat symmetrically outwards. This is exactly what you’re aiming for when readjusting.
• Check the resistance: Measure the ohm value after each pulse. If it fluctuates significantly, there is still a contact issue. A stable value indicates that the coil is seated correctly.

If the hot spot persists despite several attempts, it is better to rebuild the coil than to keep readjusting it. Bent or overheated wire permanently loses its properties.

Is a hot spot dangerous for the battery?

A single hot spot is not a short circuit in the strict sense, but it puts more strain on the battery than a clean coil. Modern battery mods with protection circuits handle this. With mechanical mods without protection, you should never vape with a visible hot spot.

Why does my coil glow unevenly even though the wraps are neat?

This is often due to the wire itself or a loosely tightened clamping screw. Check the posts, clean them with isopropyl alcohol if necessary, and tighten the screws evenly. If that doesn’t help, re-wrap with fresh wire.

Can I fix hotspots on mesh coils?

No. Mesh strips cannot be readjusted like traditional coil wires. If a mesh coil glows unevenly, it is usually worn out or already damaged and should be replaced.

How often should I check the coil?

It’s worth doing a pulse test every time you change the e-liquid and at the latest after changing the wattage. This allows you to spot hotspots early on, before they affect flavour and vapour production.

A hot spot coil is no cause for panic, but rather typical feedback from the coil: it needs a quick readjustment. If you wind the coil neatly, compact the coils carefully and ensure the connections are secure, you can get the uneven glow under control. For replacement coils, suitable wire and pre-built atomiser heads, it’s best to browse our selection of coils and builds – there you’ll find materials for every setup, from beginner pods to RDAs for experienced builders.