Smeg A1 thermal fuse

[Neil P]

Hi – I have a smeg A1 multifuel 90cm cooker which suddenly cut out when I was using the fan/grill. It seemed like the thermal fuse had blown and when I continuity tested it looked like it. I ordered a new one from UK Whitegoods, relaced it but still no joy. Gas ignition works just no oven/grill or fan. The device is a rectangular ceramic one which is clamped behind the cooling fan cut-in thermostat. Interestingly some websites discribe this as a resisitor not a thermal fuse, but UK whitegoods and Servevast both describe it as a thermal fuse. It does indeed have some resistance – 6.8kohm, which is what is stamped on the device (7w6k8j). Interestingly the one I took out, which is rated 6.2kohms, actually has a resistance of 1.8Mohm! From experience I expected an untripped thermal fuse to have no resistance, not even 6.8k. Can anyone help? Getting hungry….

[Neil P]

…incidentally it is not the timer. I bypassed that years ago (though would love to find the right replacement…)

[electrofix]

some smeg cookers use a resistor to slow down the cooling fan

Dave

[electrofix]

the only stat i can find that seems relavent is

818730567 1 THERMOSTAT SAFETY 160°C

as you say it should read 0 ohms when tested so you need to find it

Dave

[kwatt]

Firstly, is it an original A1 from the late 1990’s, nothing after A1 as there are a number of them? That’s important.

Then there’s the resistor in some, a cooling fan stat and an overheat stat but firstly you need to establish what A1 it is and then look at the layout of it.

K.

[Neil P]

Thnaks both of you. The rating plate is missing and I bought it s/h, but from looking at ll the manuals I’m pretty sure its an A1 with no extra numbers. 5 burners, offset spit drive. It makes sense that there’s a resistor to control fan speed especially as its clamped to the cooling fan thermostat! Bascially I was going by the website which offered me what turns out to be a resisitor but was clearly described as a thermal fuse! At that point I stopped searching the guts of the cooker but will now have another look.

[Neil P]

OK. There is 1 more thermostat reading 0 ohm. It’s inscribed L140-20C, so I assume its should normally closed then opens at 140deg C. But it doesn’t look like any I can see in that it is mounted direct to the back plate with a threaded stud. Most on the net have 2 wings but I suppose I could drill a couple of mounting screw holes. Full inscription is 84T31 L140-20C 48032 J9711. Its a Kema. Slightly reluctant to not replace like for like…

[kaibart]

Post a picture with a public link so we can see the part is easier

[kwatt]

No rating plate is not good at all.

Assuming it’s an original A1 then depending on the serial number it uses:

https://shop.ukwhitegoods.co.uk/818730567-smeg-oven-cooker-safety-thermostat

Or:

https://shop.ukwhitegoods.co.uk/818731042-smeg-cooling-fan-control-thermostat

And:

https://shop.ukwhitegoods.co.uk/ty60-cut-out-thermostat

https://shop.ukwhitegoods.co.uk/806890292-smeg-oven-cooker-thermal-fuse

K.

[electrofix]

if there is a reading through the stat means its not faulty

you need to trace the wiring
some smeg cookers have a plug to connect the wiring to the top of the cooker. had these fail a lot
check the oven selecter sw these are common failure

Dave

[Neil P]

it’s reading zero ohms, Dave, so I guess it’s faulty. Assuming its a cut out (and not a cut-in like the cooling fan device). Is there any reason why I can’t subsititute a different 250v 140degC device, since it doesn’t look like any of the options posted by Kwatt? Here are some images:

https://flic.kr/p/2kYSMyu
https://flic.kr/p/2kYTTbG
https://flic.kr/p/2kYQhSR

Yes, no rating plate is a PITA. Bought s/h from ebay and I suspect it may be a bit of a Frakenstein! But it is basically an A1.

Thanks for weighing in everybody.

Neil

[electrofix]

zero ohms is good not faulty
if the fuse in your fuse cupboard was zero ohms its good its only faulty when its reads millions of ohms

that is not your fault

Dave

[Neil P]

doh! That’s what I meant. There is no continuity!

N

[electrofix]

so its not Zero ohms

well as a test link the 2 wires together and it should come on. Just make sure the wires cant touch anything

Dave

[Neil P]

OK Back to square 1. On the back of the cooker are 2 thermal overload devices and a resistor. I’ve now tested both devices on the bench with the aid of a hairdryer and another oven. They both work fine. Top one is a 70deg cut in and powers the fan which works fine. Bottom is a 140deg cutout and is, as it turns out, OK. May last resposne was when I was away from the cooker so couldn’t confirm what i was tellign you, but in fact my multimeter reads 0L when there is no connection and I was relyng on my memory! I can find no trace of a thermal fuse. What whitegoodsUK sold me as a thermal fuse is in fact a resistor which Dave pointed out is to control the fan speed. The old one of them is indeed faulty so still needed replacing. It has a resistance in the megohm range (should b 6k2)! I think that has failed and allowed the oven to overheat badly (until the cut out operated) while I was using the grill. So, as Dave also pointed out, the next place to look is the selector switch. It is a very hot mess! There are signs of burnout on the back two contacts. I suspect it may have failed when the cooling fan failed. Cetrainly some of the back contacts do not seem to be making properly. I’m not 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} about the switch but all the other wiring looks intact. I think the best bet is to get new one of those. I’m reluctant to take the old one out first as I really need to swap 1 connector at a time. I think I’ve been down a rabbit hole because of my insistance that there was a thermal fuse.

[Author]

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