SAFETY WARNING: Gas hobs are gas appliances under the Gas Safety (Installation and Use) Regulations 1998. Only a Gas Safe registered engineer may open, repair, or replace parts on a gas hob. This article helps a tradesperson identify which fault category is present so the right specialist or replacement part is arranged — it is not a DIY repair guide. If you smell gas at any point, stop, ventilate, do not operate switches or naked flames, and call the National Gas Emergency Service on 0800 111 999.

Summary

"The hob won't light" covers a wide range of underlying faults, and guessing wrong wastes a visit or, worse, means someone pokes around inside a live gas appliance without the competency to do so safely. The purpose of this guide is triage: work through the visible, non-invasive checks (does the spark happen? does gas smell present? is another burner affected?) to narrow the fault down to one of the four categories above, then hand off to a Gas Safe registered engineer with a clear description of what was observed.

This matters for two reasons. First, speed — a Gas Safe engineer arriving with "the spark clicks but no gas smell at any burner" already knows to start at the gas supply/ECV rather than stripping every burner head. Second, safety — the boundary between "things anyone can visually check" (is the ECV open, is the burner cap seated correctly, is there visible food debris in the injector) and "things only a Gas Safe engineer may touch" (removing burner components, testing the gas valve, replacing a thermocouple) needs to be respected absolutely. This guide draws that line explicitly at every step.

The fault categories map onto the ignition chain of a typical gas hob: spark generator → electrode → gas valve/tap opens → gas reaches burner and injector → gas ignites at the electrode spark → flame heats the thermocouple/FFD → FFD holds the gas valve open. A fault anywhere in that chain produces broadly similar symptoms from the user's point of view ("it won't light" or "it lights then goes out"), which is exactly why a structured diagnostic approach matters more than guessing from the symptom alone.

Key Facts

Quick Reference Table

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Symptom Fault category Non-invasive check anyone can do Requires Gas Safe engineer
No click, no spark at any burner Spark ignition — power/module Check ignition battery (if battery-powered); check other burners Yes — electrode, module, wiring
Click/spark heard but no flame Gas supply / ECV Check ECV is open; check if boiler/other gas appliances also affected Yes — supply pressure, valve, injector
Spark and gas smell, but no ignition Spark ignition — electrode fault Visually check for spillage/residue bridging the electrode Yes — electrode clean/replace, gap check
One burner won't spark, others fine Localised — that burner's electrode/module Check for food debris/liquid on that electrode only Yes — electrode/module for that burner
Burner lights, then dies after a few seconds Thermocouple/FFD not holding Confirm knob was held in for full hold time (10–15s) before release Yes if it still fails after correct hold procedure
Flame uneven, some ports dark, yellow/orange tips Burner/injector partially blocked Visual inspection for spillage/debris in visible burner cap Yes — injector clearance, burner strip-down
All burners dead, boiler also not igniting Gas supply upstream Check ECV, check meter, check for a known supply interruption Yes — supply-side diagnosis
Strong gas smell present Gas leak — STOP Ventilate, do not operate switches, evacuate if strong Emergency — call National Gas Emergency Service 0800 111 999
Hob recently converted between gas types Injector mismatch Check data plate category against actual gas supply Yes — correct conversion kit required

Detailed Guidance

Before anything else — the gas smell check

Before working through any diagnostic branch, confirm there is no gas smell at the hob or in the room. A hob that "won't ignite" with a persistent gas smell present is a potential gas escape, not a routine ignition fault — stop immediately, do not operate any electrical switches (including the ignition itself) or use a naked flame, ventilate the area, and call the National Gas Emergency Service on 0800 111 999. Only proceed with the diagnostic tree below once a gas leak has been ruled out.

Decision tree

GAS HOB NOT IGNITING — start here
│
├── Is there a gas smell present?
│     │
│     ├── YES ──► STOP. Do not operate switches. Ventilate. Evacuate if strong.
│     │           Call National Gas Emergency Service: 0800 111 999
│     │
│     └── NO ──► continue
│
├── Are OTHER gas appliances (boiler, gas fire) also affected?
│     │
│     ├── YES ──► Suspect gas supply upstream of the hob
│     │           → Check ECV is open
│     │           → Check meter / for known supply interruption
│     │           → Gas Safe engineer for supply-side diagnosis
│     │
│     └── NO ──► Fault is likely local to the hob — continue
│
├── Does the ignition spark/click when you turn the control knob?
│     │
│     ├── NO SPARK / NO CLICK
│     │     ├── Battery-ignition hob → check/replace ignition battery
│     │     ├── Mains-powered ignition → check hob is plugged in / powered
│     │     ├── Only ONE burner has no spark, others work
│     │     │     → localised electrode/wiring fault on that burner
│     │     │       → Gas Safe engineer
│     │     └── ALL burners have no spark
│     │           → ignition module/wiring fault
│     │             → Gas Safe engineer
│     │
│     └── SPARK PRESENT (click/spark visible or audible)
│           │
│           ├── Does gas ignite at all (brief flame, even if it dies)?
│           │     │
│           │     ├── NO IGNITION despite spark
│           │     │     ├── Visually check electrode area for spillage,
│           │     │     │     food residue, or liquid bridging the gap
│           │     │     │     → clean gently if accessible and try again
│           │     │     │       (do NOT dismantle the burner or gas
│           │     │     │       components — surface clean only)
│           │     │     ├── Check gas is actually reaching the burner —
│           │     │     │     confirm ECV open, confirm other burners work
│           │     │     └── If spark is confirmed present and burner area
│           │     │           is clean, and no ignition — Gas Safe engineer
│           │     │           (electrode gap, injector, or gas valve fault)
│           │     │
│           │     └── IGNITES then goes out after a few seconds
│           │           │
│           │           ├── Was the control knob held in for the full
│           │           │     hold time (approx 10-15s)
│           │           │     model] before release?
│           │           │     ├── NO → retry, holding the knob in fully
│           │           │     │         for the correct duration
│           │           │     └── YES, still goes out
│           │           │           → thermocouple/FFD not heating or
│           │           │             holding correctly
│           │           │             → Gas Safe engineer (FFD/thermocouple
│           │           │               fault — SAFETY CRITICAL, do not
│           │           │               bypass or defeat the FFD)
│           │
│           └── Flame appears uneven — some ports lit, others dark,
│                 yellow/orange tips instead of blue
│                 → burner/injector partially blocked
│                   → visual check for spillage in the burner cap area
│                   → Gas Safe engineer for injector clearance/burner
│                     strip-down if visual clean doesn't resolve it
│
└── Was the hob recently serviced, converted, or is it second-hand /
    newly installed?
      → check data plate category (I/II/III) and gas type (G20/G30/G31)
        against the actual supply
        → mismatch = injector/conversion fault
          → Gas Safe engineer — correct conversion kit required,
            do not attempt to run a mismatched appliance

Spark ignition failure — what a tradesperson can and can't check

The only things safe and appropriate for a non-Gas-Safe tradesperson to check here are: whether the hob has power (mains or battery) reaching the ignition system, whether an ignition battery needs replacing (if the model uses one — check the manufacturer's manual for battery location), and a visual check for obvious spillage or liquid bridging the visible part of the electrode. Everything past that — testing the electrode gap, replacing an electrode, tracing ignition module wiring, or opening up the appliance — is gas work and must go to a Gas Safe registered engineer. The diagnostic logic (electrode gap, ignition lead resistance, module output) closely parallels boiler ignition fault-finding — see boiler ignition parts for the underlying principles, though the specific components and access differ on a hob.

Gas supply and isolation — the checks anyone can do

Before assuming a hob-specific fault, rule out the supply side:

Anything beyond these checks — testing supply pressure at the hob's own isolation point, checking the hob's internal gas valve, or investigating a suspected pipework fault — is gas work for a Gas Safe registered engineer.

Burner and injector blockage — visual checks only

A burner that lights unevenly (some ports producing flame, others dark, with yellow or orange flame tips instead of the expected blue) is a strong indicator of a partially blocked burner or injector, usually from spilled food, boiled-over liquid, or general kitchen residue. A tradesperson can visually inspect the burner cap for obvious debris and gently clean the visible burner cap/crown per the manufacturer's cleaning instructions (most burner caps lift off for cleaning as routine maintenance). If cleaning the visible parts doesn't resolve it, the injector itself may need clearing or the burner may need stripping down — this is Gas Safe work, since it involves the appliance's internal gas-carrying components.

Thermocouple / FFD faults — the safety-critical category

If the hob ignites but the flame goes out shortly after the control knob is released, first rule out simple user technique: most FFDs need the knob held in for roughly 10–15 seconds to let the thermocouple heat sufficiently to hold the safety valve open on its own. If the correct hold procedure has been followed and the flame still won't stay alight, this points to a genuine thermocouple/FFD fault — the sensor isn't heating correctly, isn't seated correctly against the flame, or the FFD mechanism itself has failed.

This is explicitly a safety-critical fault category. Never attempt to bypass, defeat, or hold open an FFD that isn't working correctly — its entire purpose is to cut gas flow if the flame is extinguished (draught, boil-over, or the user walking away), preventing unburned gas from continuing to flow into the room. A non-functioning FFD found during any inspection must be flagged immediately and the appliance should not be used until a Gas Safe registered engineer has repaired or replaced it.

Injector mismatch — second-hand and converted appliances

If the hob is newly installed, second-hand, or has recently been serviced/converted, check the data plate for its stated appliance category and gas type against the actual gas supply in the property (natural gas G20, or LPG G30/G31). A hob fitted with the wrong injectors for the supply gas type may ignite poorly, unevenly, or not at all, and even if it does light, it may be running an unsafe air-fuel ratio. This is not something to test by trial and error — a category/gas type mismatch requires the correct manufacturer conversion kit fitted by a Gas Safe registered engineer. See cooker installation for the full category (I/II/III) breakdown.

Frequently Asked Questions

Can I clean the hob burners myself, or does that count as gas work?

Routine surface cleaning of removable burner caps/crowns per the manufacturer's cleaning instructions (the kind of cleaning a homeowner does regularly) is not gas work. Anything involving removing fixed components, accessing the injector itself, working on the gas valve, or disturbing any gas-carrying joint or connection is gas work and must be done by a Gas Safe registered engineer.

The hob lights fine but goes out as soon as I let go of the knob — is that a fault?

Not necessarily. Most FFD-equipped hobs need the control knob held in for a short period (commonly around 10–15 seconds) after ignition to let the thermocouple heat up enough to hold the gas valve open on its own. If the flame consistently goes out even after the correct hold time, that points to a genuine thermocouple/FFD fault requiring a Gas Safe registered engineer — do not attempt to work around it by holding the knob for longer than instructed or defeating the safety mechanism in any way.

One burner won't ignite but the others work fine — is this urgent?

It's not usually an emergency (unlike a gas smell), but it should still be treated as a fault requiring a Gas Safe registered engineer, not ignored or worked around. A localised fault on one burner is most likely that burner's electrode, a blocked injector, or a localised FFD fault — all are within the scope of a normal appliance repair, but none should be diagnosed or opened up by anyone without Gas Safe registration.

Is it safe to keep using the other burners while one burner has a fault?

Generally yes, if the faulty burner simply won't ignite and there's no gas smell — the fault is most likely mechanical/electrical (spark) or a blockage, not a leak. However, if there's any gas smell from the faulty burner even when it's turned off, or if the FFD isn't holding correctly on that burner, stop using the whole appliance and get a Gas Safe registered engineer out before continuing to use any part of the hob.

Why does the hob only click but never smell of gas, even briefly?

This points to the gas not reaching the burner at all — check the ECV first, and check whether other gas appliances in the property are also affected. If the ECV is open and other appliances are working normally, the fault is most likely local to the hob's own gas valve or supply connection, which is a Gas Safe engineer diagnosis (isolation valve, hob's internal tap, or a blocked/kinked supply connection).

Regulations & Standards