Fault finding: An art form really!

Critical thinking in problem solving!

Not all technicians are equal in this area!

OVEN FAULT FINDING

Effective problem-solving in the context of oven repair demands a robust application of critical thinking. This skill set allows

technicians to navigate through complex diagnostics, yet not all are equally proficient, which can lead to varied outcomes in repair effectiveness and cost-efficiency.

What We Do Not Offer:

Avoidance of Cooking Events: Our focus is on the mechanical and electrical aspects of your oven, not on culinary outcomes. We handle objective, observable deviations from standard operations. We do not:

Validate Cooking Recipes:

Statements like "the recipe states the oven must Be at 180 degrees for 20 minutes" are beyond our scope. We cannot verify cooking results because they involve subjective elements like taste, smell, or perceived cooking times.

Practical Implications:

Cooking involves variables like food density, oven load, and ambient conditions, which we do not control or measure. Instead, we focus on measurable parameters such as temperature accuracy, heating consistency, and electrical integrity.

Subjective Expectations:

Concerns like "it's taking too long to cook" or "it's too hot" are starting points, not endpoints. For effective diagnostics, we need precise measurements:

Example:

Instead of "it's too long," inform us "it took 10 minutes to raise the temperature by 20 degrees." This type of feedback allows for more targeted diagnostics.

Customer Role:

We encourage customers to use timers and thermometers, which are cost-effective tools for providing us with concrete data.

Manufacturing Misconceptions:

Manufacturers' claims can sometimes mislead:

Fan Forced Cooking: While it aims for even heat distribution, physical barriers like trays or the oven's shape can impact this.

Oven Door Safety:

Doors are designed to be less hot to prevent burns, but they can still reach high temperatures. Always refer to the manual for exact temperature specifications if available.

Fan Noise:

The decibel level for normal operation isn't usually specified, making judgments on "excessive" noise subjective without guidelines.

Cleaning Services:

We do not engage in cleaning during repairs due to safety and efficiency:

Safety Concerns: The sharp edges of stainless steel panels or the potential for glass to implode if mishandled are risks we mitigate by keeping our work area controlled.

Odor Diagnostics:

Smell, while an indicator of potential issues like overheating or failing components, varies greatly between individuals:

Subjectivity of Smell:

What might be an off-putting odor to one person could be benign to another, complicating diagnostics.

Fault Finding

Diagnosing oven problems

DIAGNOSTIC METHODOLGY

Deductive Reasoning:

This is applied when we can logically infer from known facts. For example, if a fan motor's circuit is open, it logically won't operate unless closed. We use resistance measurements to confirm such conditions.

Inductive Reasoning:

When the fault isn't directly observable, we infer from other components' health. If all else is functioning, the PCB might be the issue, though this is a probability rather than a certainty:

Testing Limitations:

Diagnosing a PCB involves checking all related components, which is time-consuming and not always feasible in a field service context.

Economic Considerations:

Cost vs. Benefit:

If diagnostics cost as much as or more than replacement, it often isn't economically viable. For example, if diagnostics total $400 and a new oven is $650, many would opt for replacement:

Decision Factors:

Age of the appliance, its condition, brand reputation, and the cost of new similar models all play into this decision.

Practical Diagnostic Steps:

Initial Observation:

We start with what's visible or easily measurable, like replacing a visibly worn hinge or a cracked element.

Incremental Testing:

We might repair what's apparent first, then test to see if issues persist, adjusting our approach based on new findings:

Example Case:

Replacing hinges and an element only to find the thermostat is faulty after heating the oven, illustrating how faults can reveal themselves progressively.

Temperature and Time:

We might need to heat the oven to verify thermostat function, which requires time for cooling before further work, affecting efficiency.

Electrical Checks: We use various tests like resistance, micro-ohm readings, and thermal imaging to pinpoint issues without immediate disassembly.

Live Testing: Some issues only become apparent when the oven is operational and hot, necessitating patience and sometimes multiple visits:

Scenario:

An oven might trip a safety switch only after extended use, requiring us to return for additional diagnostics, often involving Checking for earth leakage or insulation issues under operational conditions.

Electronic Diagnostics

Need a new Electronic Control Board; read on!

ELECTRONIC PARTS

Risks associated with fitting electronic parts

So, we’ve had quick look at your oven/stove and advised it is likely a “Control Board” fault. “Likely” being the operative word! Because, no one in our industry does diagnostics on a faulty control board. To do this takes schematics and component specifications and expensive test equipment that is better suited to a lab than a van.

Further, the suppliers of the electronic parts will not refund any electronic parts once removed from its packaging. And for good reason, PCB’s are electrically sensitive, and can be damaged by inline electrical parts, or static electricity etc. Suppliers have no way of knowing what happens to the PCB once removed from its package, so they can’t or won’t take these items back.

Deductive reasoning

Not to get to technical; but for most oven/stove faults, we use deductive reasoning. Which basically means we can test certain conditions of a device which will give us a high probability that the device is faulty or not. For instance, a fan motor with an open circuit will not work unless the circuit is closed. It’s straight forward, we measure the resistance and we look for a specific result.

Simple example (Wikipedia)

An example of a deductive argument:

All men are mortal.
Socrates is a man.
Therefore, Socrates is mortal.

The first premise states that all objects classified as “men” have the attribute “mortal”. The second premise states that “Socrates” is classified as a “man” – a member of the set “men”. The conclusion then states that “Socrates” must be “mortal” because he inherits this attribute from his classification as a “man”.

Inductive Reasoning

Inductive Reasoning is basically the opposite of Deductive Reasoning. Inductive reasoning starts with a conclusion and deductive reasoning starts with a premise. Inductive reasoning moves from specific instances into a generalized conclusion, while deductive reasoning moves from generalized principles that are known to be true to a true and specific conclusion.

We use this logic to deal with an unrepresented fault. In other words where we can’t specifically test the PCB for a fault, we test the rest. If the rest is okay; then the PCB is the most likely the culprit. Most likely being the operative word!

But to prove a printed circuit board (PCB) is faulty means we must spend the time verifying the other electrical devices like the are correct. To do this we rely on resistance readings, micro-ohm reading, thermal scans, temperature readings etc. This can mean having to isolate each device and verify the correct resistance readings or other readings. Sadly, resistance is only one element of ohms law. Which means it doesn’t provide absolute positive proof that the device is functioning correctly. Same with a thermal reading, a low differential reading might imply no cause for alarm. However, using a different cooking function might change the current being drawn is just enough for what is known electrically as the pinch effect to kick in, which can then dramatically vary the differential reading without changing the temperature range. Variables are the crucial factor in determining an unrepresented fault – inductive fault finding.

Economics

Unfortunately, the cost of the diagnosis time can be as expensive as (and sometimes more expensive) than the repair itself and generally prohibits an economical outcome.

Example: (not real values)
Call out		$100
Diagnosis Labour	1 1/2 hour	$165
Electronic Board		$220
Installation Labour	1/2 hour	$55

Total		$540

Given the cost of the machine when new was say $650.oo, it is difficult to justify proceeding with the above repair.

There are many factors that would drive any final decision, such as age, condition, brand (original value), new price etc. For instance, if the machine was just 2 years old and a power outage had caused the PCB to be damaged then it might be sensible to repair the machine. But if the machine was 7 years old and was not in good nick then repairing the machine would not make much sense.

So, the reason this page exists is to save our technician from having to spend 15 minutes trying to explain these details so that you can make an informed decision. And to advise you (the customer) that if you do decide to go ahead and replace any electronic part such as the PCB, we won’t be held liable for the outcome. And once we remove the electronic part from its packaging, you the customer are liable to pay for it regardless of the outcome. Further the electronic part cannot be returned.

To diagnose or not?

We attend your home and quickly advise the hinges need replacing and one of the elements is down to earth. We tally it up and quote $300 (not a real price). We change to parts and start the testing process, while we do the paper work. This would be the average outcome of 80% of our work. But the other 20% when we get the oven going, we find the thermostat is unable to control the temperature. In hind sight everyone would agree the thermostat should have been checked before replacing the element. And, we won’t argue! In hindsight that’s correct. Setting that aside, you decide to proceed as it’s still economical to replace the thermostat. Great, oven is running while we complete the paper work. Ohhh Nooo, the fan starts to make a horrible noise after it has been hot for a while. In hindsight it would have been smart to test the fan before doing the element, hinges and thermostat. Again, we can’t disagree! The only caveat being the term “Hindsight”. It’s an expensive oven and changing the fan motor is still the most economical choice. We do the paper work all over again, the oven is now ticking away beautifully. We take payment and get on our way to our now late next job! On the way to our next job, you call and tell us the unit has tripped the safety switch as you have been running the oven since we left to give it a good test. We make a time and return, only to find the oven working fine. Grumpy, both of us, we agree it seems to be working fine and you pay for a wasted call. Sure, enough to add injury to insult you call about an hour later and advise the oven has tripped the breaker again. We make a time and come out again. This time though we start the diagnostic process.

What a horror story! Each step in the above process is a progression toward this almost absurd and rare as rocking horse pooh event. And for sure, somewhere along that progression it would have been smarter to start with diagnosis. However, there are factors that have bought us all to this horror point, the customer knew that the fan was noisy when it gets hot, but they didn’t think to mention that while we were dealing with the more obvious first issues. The customer also new that the oven tripped on the odd occasion, but never thought this was relevant to our approach; “diagnose or not”. Equally, we don’t experience this horror event very often. Hence, we let our guard down and do the mundane, routine repairs most days, weeks, months sometimes years before another horror event comes around to shock us back into reality. Things can go wrong and it’s no ones fault. Why, you ask didn’t you start with diagnosis! Well, another very good reason is “hot”! Yes, ouch that’s hot! Many difficult to find faults only present under hot conditions for some considerable time. Sometime hours before they present. And no one wants to pay for tests that don’t contribute to a determination. While we carry Adelaide leading test capability, such as Thermal imaging, Micro Ohm contact testing, live mA recording, ramp RCD testing, tachometer readings etc. These are not cheap processes and may not each be necessary. At the beginning of the above horror show, we might have started with a temperature test to prove the thermostat works correctly, which means the oven would have been “hot” eliminating our ability to replace the thermostat until the oven cooled. This process would have probably identified the noisy fan as well. But would not have uncovered the earth fault. That requires alternate test methods. In the first part of the process, we have to determine if the oven is at fault or if the circuit is compromised. Often a safety switch protects a variety of circuit. If you have a fridge, toaster, dishwasher and kettle all on the same circuit, each of this might contribute to a cumulative effect causing a trip. Add to this the fact that almost no RCD trips at 30mA as designated. Most trip around 25mA. Then if we divide equally the leakage for each contributing circuit it may only be allowing 5mA of leakage for the oven. Today it is regulation that every oven must be under its own RCD allowing a full 30mA. If this were the scenario then possibly the leakage of the oven might never be an issue. Once we have determined it is not a compromised circuit, we then need to conduct an insulation test. This would identify say 80% of earth faults. But, in our horror story, not the case. To find this fault we need to conduct a live mA leakage test on each component of the oven. Again, the operative word being “hot”! We already know now that the hot condition is a prerequisite of this fault presenting itself. To check each device while the oven is in its hot state is no minor feat. In point of fact, by this stage in the proceedings we have probably well past the repair cost of the overall job. Hence the reticence for proceeding down the diagnostic process first.

This isn’t intended as a means for you the customer or even us to determine which step and when to apply it. The factors that influence these choices are many and varied. If you have a Bunnings $500 oven then most of that is out of the ball park at element and hinges.

Bottom line, we do our best and hope the horror story remains rare! Bearing in mind our best compared to most is competitors is significant in its own right. Many wouldn’t know how to apply half the test mentioned here, much less have the threshold data for determining what the results mean.

We don't use cooking to fault find

Our testing involves: temperature, time, current, voltage, earth leakage etc.

TECHNICAL REFERENCE POINTS

We use recipes as a reference point!

Ovens at their core are just boxes with elements, fans and a thermostat to control the heating temperature. We are mere technicians and don't claim to be qualified chefs or cooks or other recipe worshippers. If the oven seals, the fan runs, the correct temperature is achieve, then most of what we can do is rendered pretty useless. What we don't do is deduce why a certain recipe does or doesn't result as the creator intended.

The reasons for what might be causing a certain cake to not come out exactly as intended, can be many and varied. We can remove most of the oven contribution to the problem quite efficiently. What we can't do is prove to the "baker" that it's not the oven. There really aren't that many factor we can change that will solve all cooking frustrations.

When the customer says that the cake is taking longer than normal to cook, or isn't cooking evenly etc. there are really only two outcomes.

1. The oven is faulty and we can reasonably fix that within a short period of time. Or

2. It's not the oven. Mmmm I hear; and then the enigmatic "but why" escapes the cooks lips and we want to run for the hills!

The variables on the cooking side of the process are many times more than the oven's operational considerations. If we consider the most basic criteria for an oven cooking correctly, temperature is the most significant. So long as we can establish a consistent cooking temperature, that's almost 80% of the issue dealt with. On the recipe side there are many more unknowns. What was the temperature of the product before being put in the oven. What was the moisture content of the product? Because a cooking event is really only one process; removing moisture!

When we think about baking a cake, who's to say the recipe ever produced a consistent result as seen in the pretty marketing image. What size egg was used? What type of flour was used i.e. protein content? Was the oven at temperature when the product was placed in the oven or bought up to temperature? Was a fan forced setting used, or perhaps a fan assist setting. Was it gas that was used when producing the recipe? Was it a 900mm oven or a 600mm oven. The variables are so many and the time it would take to resolve each variable is significant compared to the cost of replacing the thermostat.

What we hope this dialogue will do is give our customers a reason behind the many questions we probably asked when you said the cake isn't cooking like it used to. And, when we charge you for confirming the oven is working correctly; it must be related to the recipe and expectation that we can't help with, we don't want to end up being blamed by the cook for not fixing the problem.