Shaun Dunn Whether your pilot’s gone out once after a storm or it’s dropped out three times this week, at SD Plumbing & Heating we get asked the same question either way: is this just a draught, or is something on its way out? There are only a handful of things that actually cause it, and the flame itself usually gives you a decent clue before we’ve even had a look.
If it keeps happening, something’s worn, blocked, or shifted out of position. It’s not random. The usual suspects are a draught, a thermocouple that’s dirty or on its way out, a blocked pilot orifice, or a gas supply or control valve that isn’t feeding it properly.
One thing worth clearing up before you go looking for a flame that isn’t there. Since 1 April 2005 in England and Wales, and May 2007 in Scotland, new and replacement gas boilers have had to be condensing in normal circumstances, and those boilers use electronic ignition, not a permanent standing pilot. So if your boiler’s fairly modern and you can’t find a pilot flame anywhere, that’s probably why. Nothing’s wrong.
Key Takeaways
- A pilot that keeps going out usually points to a draught, thermocouple, blocked pilot orifice, or gas supply/control valve fault.
- If the pilot lights but dies when you release the control, the thermocouple is a likely cause.
- A one-off outage can happen. Repeated outages need diagnosing rather than repeated relighting.
- Modern boilers generally use electronic ignition, so they don’t have a standing pilot to go out.
- Yellow or orange flame, soot, delayed ignition, or a smell of gas means stop using the boiler and get professional help.
Why Your Boiler Pilot Light Keeps Going Out
How often it happens tells you almost everything. Once, during a proper gale? That’s a draught, nothing more. Refusing to stay lit more than that, and you’ve got an underlying fault that needs sorting, not relighting again and again.
Common Causes of Pilot Light Failure
These are the first four things we’d check, in roughly this order.
- A draught can blow a standing pilot out directly. It’s a tiny flame, so a bit of air movement around the boiler or up the flue is all it takes.
- A dirty or worn thermocouple is one of the most common causes we see. It’s the safety probe that senses the pilot’s alight, and if it can’t do its job properly, it shuts the gas off even though you’ve lit the flame just fine.
- A blocked pilot orifice, the tiny nozzle feeding gas to the flame, leaves you with a weak flame that can’t hold itself lit.
- An inconsistent gas supply or a worn control valve can stop the pilot from getting the steady flow it needs in the first place.
Why Older Boilers Fail More Often
A permanent standing pilot usually points to an older, pre-condensing boiler, and a lot of those are 20 years old or more by now. That’s a rule of thumb, mind, not a way of dating your boiler exactly, since electronic ignition was knocking about before condensing boilers became the norm.
Age matters either way. Thermocouples wear out, orifices get dirty, and small parts start giving trouble on an older appliance. That’s normal wear and tear, not something you’ve done wrong.
Pilot Light Problems in Specific Situations
Sometimes there’s an obvious trigger: a gale, a power cut, or a pilot that behaves differently one week to the next. Each one narrows things down.
Wind Exposure and Draught Problems
Strong wind can knock a standing pilot out on its own, especially if the boiler’s close to an external door or window, or there’s something off with the flue or ventilation.
Whatever you do, don’t block an air vent or tinker with the flue to try and keep the flame going. They’re there to keep combustion safe, full stop. If draughts keep putting the pilot out, book a boiler servicing and have the ventilation and flue checked by a Gas Safe registered engineer instead.
Post Power Cut Failures and Intermittent Faults
A true standing pilot doesn’t need mains power to stay lit. The thermocouple and gas valve keep it going on their own, so a short power cut shouldn’t put the flame out by itself.
If you’ve relit it after a power cut and it won’t hold, something needs checking: the thermocouple, valve, or another component. And if it runs fine for a week before dropping out again, that’s still an intermittent fault. It hasn’t fixed itself; it’s just taking its time.
Flame Colour and Other Visual Clues
The flame itself tells you a fair bit. A healthy pilot burns steadily and wraps around the thermocouple, rather than dancing about or pulling away from it. Steady blue means the gas is burning cleanly, with enough air getting to it.
A weak, lazy flame usually points to a restricted gas feed. One that lifts away from the burner can mean a pressure or aeration problem. We’d rather test the appliance than guess from how it looks, though. Appearance gets you close, not exact.
Yellow or orange means incomplete combustion. Don’t keep relighting it to see if it clears up on its own. It won’t. Switch it off and get an engineer to check it.
Black or sooty marks around the pilot assembly, or a burner that ignites with a delayed thump, are more serious. Stop using the boiler and get a Gas Safe engineer to assess it. They’ll work out whether it needs to be isolated under the industry’s unsafe-situations procedure.
Diagnosing the Root Cause: Thermocouple and Other Components
Once you’re past the manufacturer’s normal relighting procedure, diagnosis is a job for a Gas Safe registered engineer, not a guessing game. Under the Gas Safety (Installation and Use) Regulations 1998, anyone working on gas fittings and appliances has to be properly registered.
You can check any engineer’s registration at gassaferegister.co.uk before they set foot in your house. We’d recommend doing that before using anyone you haven’t dealt with before.
Thermocouple Issues and Failure Signs
The thermocouple’s the pilot’s safety check. Once the flame heats it up, it holds the gas valve open. Let the flame go out and the thermocouple cools, and the valve shuts the gas off. That’s the whole job it’s doing.
If it’s dirty, worn, or not sitting quite right, it won’t stay hot enough to do that job properly. The symptom’s almost always the same: the pilot lights fine while you’re holding the control down, then dies the second you let go.
The part itself is small and cheap. What you’re actually paying for is the visit: someone coming out, working out that it’s the thermocouple and not something else, and doing the job safely.
Dirty Pilot Orifice and Gas Supply Problems
A weak, lazy flame that never quite wraps the thermocouple usually points at the orifice. Years of dust and soot narrow that nozzle, the gas flow through it drops, and the thermocouple can’t get hot enough to register a flame at all.
A low or inconsistent gas supply does something similar: the pilot never establishes strongly enough to hold once you let go of the control.
One thing worth checking before we even get there: is your hob or gas fire playing up too? If they are, you’ve done half the work for us and helped narrow it down to the supply rather than the boiler.
Safety Valve and Sensor Faults
A failing safety valve or flame sensor can mimic a dead thermocouple almost exactly. Both shut the gas off when no flame’s detected, so from the outside the symptom looks identical. That’s why swapping the cheapest part and hoping isn’t how we’d do it.
Wear adds up with age, so on an older boiler we’ll usually test the thermocouple, the orifice, and the valve together rather than fixing on the first thing that looks likely. Ask what was actually tested, not just what got replaced.
How to Relight Your Boiler Pilot Light
Relighting a standing pilot is one of the few things on a gas appliance you’re meant to do yourself. The controls are built for it. The exact sequence varies boiler to boiler, so whatever’s printed on your appliance beats anything written here.
- Smell for gas first. If you can smell it, stop. Don’t touch the controls, smoke, use a naked flame, or flick any switches. Turn off the gas at the meter only if you can reach it safely.
- Read the relighting instructions printed on the boiler and follow them wherever they differ from what’s here.
- Turn the control to the pilot position.
- Press and hold the pilot control, then use the appliance’s built-in igniter. Only reach for a match or lighter if your boiler’s own instructions specifically say to.
- Keep holding the control for the time stated by the manufacturer, usually 20 to 30 seconds.
- Release it slowly. If the flame goes out, wait for the interval stated in your instructions before trying again.
If it stays lit, you’re done. If it keeps dying the moment you let go, don’t try holding it for longer next time. That’s not the fix. It’s one of the classic signs the thermocouple or something else needs looking at.
Stop after the number of attempts your manufacturer gives you. A boiler that isn’t responding after that isn’t going to start responding on attempt six.
When to Call a Professional Engineer
Once you’ve followed the manufacturer’s instructions and hit their stated limit without joy, stop troubleshooting. The same goes if the pilot keeps going out on calm days, dies the second you release the control, or just isn’t behaving like it used to.
A yellow or orange flame, soot, or delayed ignition means stop using the appliance and book a boiler repair. If you can smell gas, skip troubleshooting altogether and follow the emergency procedure below.
If your pilot keeps going out, give SD Plumbing & Heating a call. We can diagnose the fault, check the thermocouple, pilot orifice, gas supply and valve, and tell you what actually needs doing. And if it’s an older standing-pilot boiler, we’ll give you a straight answer on whether it’s worth repairing or whether it’s time to start looking at a boiler replacement. Get in touch and we’ll get someone out to take a look.
