Oven Element Keeps Blowing!

Why does my oven element keep burning out??

The short answer = for many reasons!

Unfortunately the right answer is subject to many factors. Most of which can’t be answered without a proper diagnosis.

Our experience of causes (in order of frequency) is as follows:

  1. Element has gotten too hot! – Often the Thermostat
  2. Poor manufacture quality.
  3. Cooking fan stalled or running slow.
  4. Bad termination.
  5. Moisture ingress.
  6. Leaking air causing the oven element cycling rate to increase.
  7. Blocked airflow.

In reality all problems really stem back to design! All elements could be designed to last longer, by:

  • Decreasing the Watts/CM. (static elements = average 6 watts per centimeter and ventilated = 10 watts per centimeter)
  • Increase the diameter of the element from 6.5 to 8.5mm.
  • Use Incoloy rather than Stainless Steel/Steel.
  • Use better grades of Nichrome resistance wire.
Courtesy of EGO
Element Components

 

Right now we can’t ascertain build quality because none of the Manufacturers or Manufacturers representatives either can’t or won’t supply that information. If they did we could start correlating types of failures to potential causes. And while we can stipulate what would be the preferred method of build… the reality is, it would increase the cost of production and reducing production volumes. Our aim is to find the best outcome for our customers, while recognising we are in no position to influence many of these worldwide realities.

Grimwood was Australia’s last serious Oven Element Manufacturer and went into liquidation back in (2013), which means just about all elements come in from overseas. And there are 100’s of manufacturers!

So… how to choose the best of an average bunch? That’s the big question!

To do that we have to understand the significant factors that we can influence that might help improve element longevity!

Element has gotten too hot!

The surface temperature of oven elements can reach up to 840o C given the right conditions. A fan forced element can have a watts/cm of 12. Couple this with a stalled fan motor and the sheath (the metal jacket) can start to melt. But the real cause of the outer sheath failing is normally because the inner filament (the actual wire element) melts and reduces resistance and increases the current, which in electrical terms we know as the pinch effect.

Filament and powder melts into the sheath
Pinch Affect

This first melt then creates more heat causing more melting and not long after the element fails. Sometimes in spectacular sparkler like fashion. Which can keep on going, even though the power has been switched off.

Element has been allowed to get too hot.
Sparkler Affect

Or the thermostat has failed, or the filter over the fan cover has gummed up, or the door is leaking air and so the element does not cycle on and off as regular as it is designed to do.

Poor manufacture quality.

Element failure is primarily caused by poor manufacture and elements getting too hot from oven conditions. Fractures along the element normally indicate poor weld quality during manufacture. Using chemicals in the oven also degrades the condition of the outer sheath of the cheaper materials now used. But the more common cause and the one we have to try to identify is the ‘blown’ element. This is normally cause by the filament touching the outer sheath. The filament grows (a lot for the space it occupies) when it gets hot and contracts when it cools. The Magnesium Oxide (MgO) acts as the insulator and is a white powder that separates the filament from the outer sheath. Because when the filament touches the outer sheath the game is over. So all this contracting and expanding is fine if the powder is compacted evenly and the filament/sheath are concentric. However, in a cheaper less rigorous production environment this tricky process often is less than perfect. This can be visually seen when elements have hot spots from brand new.

Weak welding and cheap materials!
Poor Manufacture

Cooking fan stalled or running slow.

Fan forced elements are designed with higher watts/cm than top and bottom elements. This is because air passing over the element cools the outer surface, thus helping to limit the outer surface temperature. 550oC is the typical upper limit temprature we anticipate a fan force element will be subjected to when the cooking fan is running at its optimum. If your fan forced element has suffered a sparkler effect like event you would want to check that your fan (air flow rate) is running correctly.

No air causes the fan element to over hear
Sparkler Affect

Bad termination.

Although most element suppliers would like you to believe terminal failure is the main reason elements fail! Shock horror, it is really just an excuse (in most cases) to avoid having to change an element under warranty. Bad termination is normally only a small percentage of element failures and cannot cause or even contribute to events such the sparkler effect or blown elements or fractured elements.

However, where a bad termination has occurred it is easy to see and requires the termination to be remade. This is where repeat events can come into play. If you use low grade terminals to remake the termination the likelihood of a repeat event is high.

Bad Termination is easily recognised
Bad Termination

We struggle to get a reliable supply of good quality high temperature terminals here in Australia. The terminations we use come from Germany as many other brands look good but do not have the same quality.

Moisture ingress.

This is condition is rapidly increasing in it presentation of earth leakage faults we attend. Customer are often shocked and dismayed when a new element is installed and yet the safety switch trips again. It’s no fun having to explain to customers that this is by no means unusual these days. Element manufacturers representatives will tell you that elements are hygroscopic (they absorb moisture), however this is a false statement. What the should say is that the MgO is hygroscopic! However that does not mean the element should be! The element should be sealed. And as manufacturing technology improves we will eventually see less and less of nuisance saftey switch faults due to poorly manufactured elements. Right now though the average element is not seal to moisture and so we often have to attempt drying the elements out upon installation. This is a huge time waster for us, given we fit so many elements.  Late in 2020 the Technical Regulatory made it mandatory that all new oven/stove installations will have a  Residual Current Device (RCD), better known as the ubiquitous safety switch. Originally oven and fridges were exempt from RCD protection because they are know to cause nuisance tripping. But safety has won the day and so they are no longer exempt. Meaning these earth faults are presenting more often and will continue to increase in numbers as those ovens that weren’t protect by RCD’s slowly migrate to being protected. Cleaning events, or long periods of no use are also a facet of moisture and RCD trips. Another factor is that in most modern ovens there are sometimes 3-5 elements in them. We normally only use 1-2 on a regular basis. So when one of the predominantly dormant elements is engergised for the first time in a while the moisture travels to the nearest exist and causes a bottle neck. This concentration of water causes what we call an earth fault, which when concentrated enough reaches a level where the safety switch activates ( greater than 30mA). This can happen in the first few minutes of turning the element on or longer in some cases.

Leaking air causing the oven element cycling rate to increase.

As we previously explained, the filament expands and contracts in a limited space. In a proper functioning oven the thermostat (analogue thermostat permissible average variation +/-10%) turns the power off to the element when the desired temperature is reached. Now subject to the quality of the ovens thermostat,  insulating properties and any air leaks we expect an oven set to 180oc to rise to about 190-200oc and then drop back to 160-170oc before turning back on again. The time it takes for this variation in temperature is directly related to the quality of the oven. The longer it takes the better the oven. If air leaks from the oven space then the thermostat turns on and off at a greater rate. And so the expansion and contraction of the filament increases.

Could be excessive cycling
Hot Spot

Remember the filament is just a piece of wire with properties to handle heat better than every day steel. The insulation helps to protect the filament from movement and oxidation. If the rate at which the filament expands and contracts or better now viewed as flexing, is say doubled, then you can assume the life of the element will be halved. Sooner rather than later the filament is going to either snap or touch the outer sheath.

Blocked airflow.

Customers often use aluminum foil to cover roasts and other food products in the oven, which is fine provided it stay put.  But in the fan forced ovens this foil can tear and fly loose and get caught in the fan or its vents.

Some oven are provided with gauze covers which filter debris such as oils and fats etc. These get clogged over time and reduce the flow of air. We recomend you remove them unless you find it is improving the state of your cooking or cleaning.

How to select the best value for money element?

We now have a better understanding of what causes element failures. Sadly 80% off the causes we have no control over. The best thing we can do is choose manufacturers who we experience the least amount of faults with. Only through doing large volumes of element replacements can we really form a sound opinion regarding the quality of an element.

Bottom line; choosing the best manufacturer is a moving target. Many of the large brand names we have come to trust and respect are outsource large volumes of element manufacture to cheap labour countries. And they move these arrangements more often than ever these days.

Diamond or Glass
Diamond or Glass

We have used EGO elements in most of our jobs over the last 10 years or so. However, EGO (a German company) has had to get in the game so to speak in terms of being competitive. And almost all who buy element are only interested in the price and because the selling agents can’t seem to understand that promoting better quality element and their attributes we are sadly having to concede their market dominance as the preferred manufacturer is now under scrutiny. We struggle to make quick judgements about which brands to use as a minimum period for an element to prove its reliability is probably 5 years. It also means having installed many of the same elements to end up with a robust judgement. Product fade I was recently told by senior industry insider is a feature rather than a defect when discussing current Chinese manufacturing, Now, let me state, I believe it has become a feature of many manufacturing blocks and is not limited to China. What the devil is “Product Fade” you ask? That’s the reduction of manufacturing costs from the first delivered products to the ongoing delivery of the same product. The first deliveries are made up of the best quality the product is ever likely be. Then over the course of time the better quality components such as MgO, Incoloy tubing, Ni-chrome resistance wire, are switched out for cheaper products. Because very few could challenge without the help of a laboratory analysis if that’s the truth of it. So it take time to learn the quality attributes of an element remain reliable over time other than in the field. Meaning it is only from changing lots of elements over a long period and adjusting stock holdings to favour the reliable elements.

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