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George-Allsorts
George-Allsorts, Senior Appliance Technicial Manager
Category: Appliance
Satisfied Customers: 1448
Experience:  A whitegoods technician with 30+ years service in Domestic Appliance Service & Repair, and General Mechanical & Electrical Repair
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I have a smeg oven which is cutting out after about 15 minutes

Customer Question

I have a smeg oven which is cutting out after about 15 minutes and then resets after a further 15 minutes. I have replaced the main thermostat and now also safety limit stat. The Fan is working OK. What do you think is the problem? It seems to be a common fault in Smeg ovens as seen by on line queries on other sites.
Submitted: 2 years ago.
Category: Appliance
Expert:  George-Allsorts replied 2 years ago.
Hello, my name is George..

Is the tangential cooling fan working? If not, check the fan and the thermostat for the fan.. If either is faulty it can cause this problem.

Moreso, check the element connections at the selector switch as if the previous element blew, it may have damaged the fingers of the selector.. This is very common.

If you need a wiring diagram then one is available by accepting the 'Additional Service' request that has been sent to you.

Kindly be patient whilst awaiting any responses from me as I'm not constantly available.
Customer: replied 2 years ago.

Sorry I had to leave home this afternoon and am only not long back and seeing your reply short time ago. I will not be able to check the oven until tomorrow. But can tell you that the fan appears to be working and oven seems ok on low heat up to about 150degreesC. However once the stat control is raised to anywhere @160degrees C or above the fault kicks in and it shuts electrical supply. The main thermostat which has been replaced is apparently working ok.

Expert:  George-Allsorts replied 2 years ago.
When I say the tangential fan I mean the cooling fan, not the circulation fan inside the oven.
Customer: replied 2 years ago.

I only remember seeing onE fan in my oven viz; the circulation fan when I was replacing those parts, which is inside the oven on the back wall so not sure where, or if there is a tangential fan in my model which is the Smeg SE375MFX5.

Pretty sure that there is only one fan , i.e the circulation fan which is visible inside the oven enclosure. Therefore not sure what George means when he mentions the other one viz; tangential "cooling" fan. Might add that I am also a retired electrical maintenance engineer with over forty years experience.

Expert:  George-Allsorts replied 2 years ago.
Is your model the one with the microwave in it?
Customer: replied 2 years ago.

No George my model is about eighteen years old and has no microwave.

It just has an upper and lower heating element, grill facilty and the fan assistance which is optional depending on the mode of cooking selected.

There is as far as I can ascertain only the main thermostat and the safety (TOC) stat which is mounted on the outside upper back wall oven oven compartment. Both of these stats as I have stated have been replaced and correctly wired

Expert:  George-Allsorts replied 2 years ago.
Thanks for that response Alex,... then a very likely culprit is the element connections at the selector switch.. since the previous element blew, the fingers of the selector may have been damaged.. This is common-place.

Check the slector and let me know what you find tomorrow
Customer: replied 2 years ago.

Ok thanks George I will do that tomorrow and get back to you. When is a good time to get you?

Expert:  George-Allsorts replied 2 years ago.
I'm off work tomorrow , but I do check in on my clients problems regularly during the day and will respond as soon as I see the need
Customer: replied 2 years ago.

Ok thanks George will check the connections on the selector switch as you have suggested and let you know if your suspicions .and diagnosis is correct. Fingers crossed, that is the problem as it is doing my head in having spent quite a few quid up to now.

Regards ***** ***** Night,

Alex

Expert:  George-Allsorts replied 2 years ago.
Good night
Customer: replied 2 years ago.

Good afternoon George,

I have now checked the selector switch which appears to be sound. There are no signs of any arcing, pitting, overheating, with all spade terminals, contacts, and wiring in perfect condition. There is also only one fan i.e the circulation fan which from what I can see is also working fine and running when oven is on.

The only other controls that I cannot be sure about is the timer control board. This also appears to be in good nick and no visible signs of burning or overheating on the components. But we never use the timer anyway as it is always on manual mode.

As stated earlier the oven seems to work ok when cooking at 150 degreesC or lower but cuts out when cooking at temperatures in excess of 160 degrees C. This could I think point back to the "new" Safety Thermostat which has just been fitted.because I can think of nothing else that would cut off the electrical supply in these circumstances. This is a real "headscratcher".

Regards,

Alex

Expert:  George-Allsorts replied 2 years ago.
Hi Alex,

I'm looking at the wiring diagram at the moment and this is indocating two fans..

One is wired as a cooling fan and is wired directly from the neutral to pin one on the output of the selector switch via a double connector on the lamp terminal

The second is wired as a cooking fan which is wired inline to the lower heating element with its input grey wire on pin 2 and its neutral blue wire heading inline to pin 6 of the selector via the lower heating element
Customer: replied 2 years ago.

Sorry George just seen your reply and am back @oven with my phone wilmake those further checks and reply to u

Customer: replied 2 years ago.

George Checked as u stated from wiring diag.My apologies there is another fan located on the back outside oven wall.Have the oven on full pelt and both fans are apparently working.

Sorry that second fan which I now think is the cooling fan is fitted on to the outer skin at back of the oven.

Customer: replied 2 years ago.

George,

Just a further update oven is sitting in middle of my kitchen floor withtop and back covers off exposing the wiring and componentsd

It is on and cooking up to 200degsC although main stat led still lit bit temp over 180C as led goes off when stat knob reduced to that temp.Oven still running and no cut off but was smell of burning shalac but only for a few mins...............further update.....Smell has gone but oven continued to cook and heat to setting of 200C for at least an hour with no problems. However it is sitting out of its housing on my kitchen floor with top and back covers off.

Both fans are functioning ok from what I can see and will only know if fault has disappeared temporarily until I refit all covers and refit unit into its kitchen housing which will be later when it has cooled down. However I have not actually down anything today other than shift the unit on to the floor and removed the covers to get a closer look and inspect the component parts that you suggested.

Maybe get in contact again tomorrow.

Regards,

Alex

Expert:  George-Allsorts replied 2 years ago.
Hi Alex... This then does dound like a cooling issue, thermostat or the selector..

Lets look atit in a logical form... There is a burning smell.. This could be the wiring attached to the thermostat, or more likely the selector..
If you heat-up the appliance to the point that the smell re-appears, then turn it off at the wall so there is no power and use your nose to detect the source... The source of the burning smell is your likely culprit..

Think also, is there sufficient air-gap surrounding the appliance...

Are you ok dealing with this without the wiring diagrams?..
If you need a wiring diagram then one is available by accepting the 'Additional Service' request that has been sent to you.

regards
Customer: replied 2 years ago.

Hi George,

Just finished my dinner which was successfully cooked in the oven albeit located on the kitchen floor and reading your reply. Yes the burning smell which has disappeared could certainly be an indication of now perhaps "intermittent" fault as the oven continued to cook for well over an hour at high temperature which it was not doing.

My thoughts are now that one of the fan motor windings are "dodgey" and most likely the cooling one which is not visible when the oven is in situ. Although It was running the whole time that I was using it with all parts exposed. I am going to now try to meter both sets of windings to check the resistances on both, because I know both stats are new and the selector switch is just a "cam" operated device which opens and closes the various selected contacts to the heating elements.

Expert:  George-Allsorts replied 2 years ago.
Hi Alex, the smell of burning shalac usually comes from the shorting of connections near to the plastic of the thermostat or selector switches, but could also come from the nylon surrounded fan windings... A nose test should snitch the culprit for you.

Please feel free to now rate the assistance given so far & return to me should you need to put two heads together any further
George-Allsorts and other Appliance Specialists are ready to help you
Customer: replied 2 years ago.

Hi George,

Have had a good "sniff" around the component parts albeit with the supply switched off, but no clues as to where that smell might have emanated. Also touched around those parts which could be overheating and again no residue heat in those areas.

Got my meter and tested the resistance of the windings on the coils supplying both fans. The cooling fan showed a resistance of 131.4 ohms whilst the circulation fan windings had a 96.7 ohms resistance. I have now refitted all covers and refitted the oven into the kitchen housing. I thank you for your assistance to date even though although the fault has "disappeared" not entirely convinced that it is due to anything that I have done since you have been advising me. Perhaps you can give me advice on the expected resistance of the winding to both fans compared to my readings, as therein could be the problem.

Anyway only time will tell so may be back on tomorrow but hopefully not.

Regards,

Alex

Expert:  George-Allsorts replied 2 years ago.
Sorry, I do not have the exact resistance values of the fans but they do sound roughly about right

Before you return everything back to the cabinet, check the area of the connections to the lower heating element, and the proximity of the terminal connections to the surrounding panels.
Also check that the terminal connections are on properly and not loose, as sparking there will also cause the same acrid burning smell
Customer: replied 2 years ago.

George that was all checked very carefully and all connections to recently fitted parts removed and refitted just in case there were any loose connections. As stated earlier only time will now tell ..........????

Regards,

Alex

Expert:  George-Allsorts replied 2 years ago.
Ok, I will be here if you need to chat.
Customer: replied 2 years ago.

OK but in the nicest kind of way I hope not as my wife wants a new oven and I cannot afford to buy a new one right now. So fingers crossed that the oven will continue to perform as it did this afternoon for another bit longer.

Customer: replied 2 years ago.

Well George,

Obviously you will probably not see this email until tomorrow.


As suspected the fault has reappeared on using the oven this evening. After about 20-25 mins cooking at 160C oven shut down.The oven stat LED had went out and within about 3-4mins as soon as LED reilluminatef the oven shut down.I waited until the oven came back on after about 10mins.Reset stat control to 140C but after about 10mins cooling it shut down again.Tomorrow I am going to short out the safety limit stat as I at least know the main control stat is working.This will at least enable time to cook properly until I can locate which fan is on the way out. Hope you agree.



Regards



Alex





Expert:  George-Allsorts replied 2 years ago.
Alex, the temperature limiter is there to protect you and your property if something goes wrong... If you are competent, you could bypass it under a controlled situation to test it, but under no circumstance can I condone cooking like that or running the cooker for any length of time in that situation..

I suggest you remove the cooker from its housing again and test it once more.. Test the cooling fan to extreme, also test the various safety switches, especially the one that controls that fan.. The fact that the oven continued to work outside of its housing must have had something to do with the issue..

Tell me; when you had the cooker out yesterday.. was the cooker sitting on the ground, or was it off the ground?

Another thing to try is to disconnect and shiel the wiring for the base element that you have just fitted and try the cooker without that base element... If you have an insulation tester, test both oven elements immediately that the power drops.

Keep a close eye on everything, especially the selector switch and fan.. Try find the souce of that smell.
Customer: replied 2 years ago.

George,

Did not expect a reply until tomorrow u must also be a "night owl" like me. When I stated that I would be bypassing the safety limit stat this would have been only temporary and always in a controlled situation as I am well aware of the consequences of doing something stupid to carry

this out in an uncontrolled environment.

To answer your question as previously stated the oven when fumctioning full pelt Sunday afternoon was sitting on my kitchen floor with top and back covers removed and totally unenclosed.Thus it would appear to be an overheating problem when all covers fitted and fully enclosed in kitchen housing.Logistically it would appear that at least one of the fans is not functioning efficiently in an enclosed situation.

Expert:  George-Allsorts replied 2 years ago.
What was the appliance sat on at the time... was it on the floor or off the floor?
Customer: replied 2 years ago.

The appliance was sat on the floor of the kitchen when it functioned for over an hour at full pelt, with top and back skin enclosures also removed. .

Expert:  George-Allsorts replied 2 years ago.
My thoughts on this pull me to either insuficient cooling from the cooling fan, or moreso the failing of the selector switch...

Keep an eye on the fingers of the selector switch when the problem occurs.. make sure one of the fingers hasn't lifted or broken connection.
Customer: replied 2 years ago.

OK and tend to agree that the cooling fan is perhaps not working efficiently even though it was seen to be running when I had the oven out of its housing and fully exposed.. The selector switch when I examined it looked in perfect condition, but difficult to have a thorough inspection unless I completely remove it.

Later this morning I am going to unscrew the cooling fan from its mounting on the outer wall and have a real good look and "sniff around "this component. There is a little bit more work in eliminating totally the selector switch but will only do this as a last resort, because as stated it does appear to be in sound condition visually from what I can see

Expert:  George-Allsorts replied 2 years ago.
Alex.. Ring me ***********