Help needed with NEFF B1920 oven

[JeffreyDoujon]

Hi All
I have a Neff B1920W0GB built in oven
Just before christmas I was cooking some food in the oven when there was a fairly loud bang and all the lights went out. The main RCD had tripped as had the “cooker” MCB, I did the normal (not right) thing and just reset both, everything came back on. After a while I went to get my dinner and found the oven cool.
I have pulled the oven out and checked the elements and both read 10’s of ohms so elements are intact. I nearly missed the overtemp cutout which had a large (over an inch dia) plasma flash mark. I measured the cutout and it was O/C so removed it.
On inspection the cutout is, to use the tech description F******, internally blown apart.
My question is this just a faulty cutout or did the element (at temp) short to ground causing really excessive current and atomising the cutout ?

I am an electronics/electrical designer and would like some input Do I replace just the cutout or element and cutout ?
Thanks
Jeff

[kwatt]

Re: Help needed with NEFF B1920 oven

Possibly just the cutout but it could be caused by a faulty oven thermostat allowing it to overheat or fan motor which would effectively lead to the same.

They do occasionally pop for no apparent reason but, most times, there’s a cause. The trick is finding the cause if there is one.

K.

[JeffreyDoujon]

Re: Help needed with NEFF B1920 oven

Hi KWatt

Thanks for the reply

The TOC seems to be a bimettalic type not a thermal Fuse
I suppose the damage could be due to opening under the 10A load becuase of a faulty thermostat
I think I’ll replace the element and the TOC and then check the thermostat with my thermocouple

Jeff

[Brains]

Re: Help needed with NEFF B1920 oven

If you can get access to an insulation resistance tester (megger), you might want to test the insulation resistance of the element and fan.

Testing the oven for insulation resistance prior to power up would be a good idea.

Remember to isolate the supply to the oven first prior to testing.

Regards

[mjjuk]

Re: Help needed with NEFF B1920 oven

I have changed just the t.o.c before but as mentioned above an insulation (megger) test should be performed to check other components

[JeffreyDoujon]

Re: Help needed with NEFF B1920 oven

Hi All

Thanks for the replies

I found a Bimetallic Thermal switch (150C) in my lab today so fitted that in place of the standard TOC
I placed a thermocouple on the mounting surface (accuracy +-2 C maybe) and a RTD in the oven (accuracy less than 0.5 C) and fired it up results were:-

Setpoint Temp RTD
100 C 98.7 C
150 C 138.3 C

200 C 185 Heat Off
180 Heat On

220 C 198 Heat off
194 Heat On

250 C (max) 232 Heat off TOC Temp TC 96 C
235 peak
230 Heat on

I’m a little confused as the TOC that was removed was rated 180 C and Neff state 130 C for this model, however 130 seems OK from the above ANy comments on this ?

I will grab the megger and test the element but it looks like it was a faulty TOC

Jeff

[Author]

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