Gas Hob Burners
Gas burners on cooking appliances, these days, are generally only used for an oven burner and of course hob burners that you will find as a stand alone built in hob and, also on the top of a cooker or a range cooker.
In the past you could also find gas grills but these have largely disappeared in domestic cooking due to the risk from CO poisoning due to the nature of a gas grill.
Here however we are concentrating on gas hob burners more than anything else.
For the most part the more common gas burners that you see on domestic hobs and cookers are very rudimentary in the way that they work however there are obviously very real safety concerns when it comes to gas products. The short of it being that, if you are not sure then get in a professional repairer to do any repairs for you as it is not a thing to be taking risks with.
There are three basic elements to a gas burner on a cooker of built in gas hob:
- The gas burner assembly
- The ignition system
- The safety system
When it comes to gas burners not staying alight as, we are presuming that the gas burner lights but then goes back out, the two that we are really concerned with are the burner assembly itself and the safety system that is in use.
Gas Burner Assembly
Most gas burners will follow the same basic recipe these days in that you will have an ignitor or spark plug, a thermocouple (explained more below), the jet, burner base, gas burner body and the burner cap or flame spreader. The terminologies can alter depending on who you take to but, in essence that’s the basics.
The whole lot sits on the burner base. This is the part that will invariably hold the jet and is mounted underneath the hob itself, with all the burner stuff off and out the way, you will usually see a sort of aluminium cup with the brass jet in the centre of that base.
On top of this site the burner body, the part with all the small holes that the gas shoots out of.
Then the burner cap or flame spreader, the flat metal cap that sits at the to top it all.
The gas is injected through the jet, mixes with air in the cup to the burner body where it shoots out under it’s own pressure, due to the burner cap deflecting it that way and you have a gas burner.
The ignitor gives a spark between the cap and the plug to light it and the thermocouple is a safety device to keep the gas on while there’s a flame.
Hob Gas Burners & Thermocouples
Gas burners come in all manners of different shapes and sizes as on a hob of any type used in built in hobs, cookers and range cookers you have traditional type round burners of various sizes, wok burners, fish burners and even hotplates on some with gas burners although, some of these are rare to see. However the basic principles apply to all.
With legislative changes for a number of years now, all these hob burners have to have what are known as thermocouples fitted by law.
The thermocouple is a metal “pipe” filled with gas that expands when the burner is lit from the heat of the burner flame. The tip of the thermocouple should always be in the flame of the burner allowing it to heat up. In turn, this lets the gas valve know that there is a flame and that the gas tap should stay open.
What happens is that when you press in the gas tap control knob then hold it for a few seconds, this is the thermocouple getting war enough to keep the gas valve open. Once warm, when you let go of the control knob, the burner operates as you would expect and stays lit.
Should the thermocouple not sit in the flame correctly or, the thermocouple is faulty, then the gas will be shut off to that burner as soon as you let the control knob go.
This is a safety feature that cannot be disabled or defeated in any way.
The take away points and probably the top problems when a gas hob burner will not stay lit are:
- Ensure that the thermocouple tip is in the flame of the gas burner
- Replace the thermocouple
Of course you could also have an issue with the gas tap however this is not common at all and the two reasons above are, for most gas hobs, cookers and range cookers, the most common issues that cause this reported problem.
Poor Flame Or Blocked Jets
Also a problem at times is a poor flame. What this causes is the flame not to reach or, not enough heat to reach the thermocouple meaning that it does not heat up enough to hold the gas tap open.
This is what a healthy flame should look like on a typical hob burner:
The most common cause of this is dirty or blocked burners, which is the part that you can easily take off to clean. All the small holes on the burner should be clean and clear, if not then even a partial blockage can lead to the thermocouple not getting enough heat and, the burner won’t stay lit.
A blocked jet can cause much the same issue however, that’s a bit harder to get to and clean out.
If you lift off the entire burner you will often see a small brass “nut” with a tiny hole in the centre of it, that’s the jet where the gas is injected. You can try to clean that with a thin wire or suchlike if you’ve cleaned the burner head etc and still have an issue.
The image below shows a typical jet right in the middle of the burner base and, as you can see, it's a bit grubby in there after years of use.
Carbon Monoxide & Burner Parts
Do please note and, this is extremely important, that if you see any yellow flame rather than clean blue as you would expect from a gas burner, do not use it as it’s not burning correctly and emitting carbon monoxide. This is bad, very bad and you will need to either clean the burner more thoroughly or replace it. If that does’t cure it then you will need help from a Gas Safe registered repairer.
The image to the right, whilst an extreme example in some ways, shows a desperately dangerous burner flame to see. This requires immediate attention.
It is also vital that any parts you replace on a burner are the proper ones for that hob or cooker, you cannot use ones not for that product due to the above as, if the gas/air mix etc is not correct then you run a very high risk of incorrect burning that can lead to all sorts of issues. Some of these issues can be life threatening so, please ensure that you order the correct replacement parts, something that we can help you with.
To get the correct parts you will need the model number at least, often more these days, of the cooker or gas hob.
For a cooker inside the oven door or in a storage drawer are the most common places to find that and they are almost always easily accessible without having to pull the cooker out. For gas hobs it’s harder as the rating plate is virtually always underneath the hob so, you need to access that to get the required information.
Due to the nature of gas parts, do not guess as that’s far too dangerous! Make sure you order the correct part/s for your product.
If you are not sure STOP!
Gas products can be dangerous, if you are unsure at all do not proceed, stop and have it looked at by a suitably qualified technician.