On 20/12/2018 13:55, Andrew Gabriel wrote:
In article ,
newshound writes:
On 20/12/2018 12:57, newshound wrote:
My Kenwood oven has two "thermostats" on the main frame, not the
standard temperature controlling ones, but apparently for
overtemperature protection.

https://www.espares.co.uk/product/es...ctur erId=435


and

https://www.espares.co.uk/product/es...cturerId= 435


The first is open circuit, the second closed circuit.

I think I would have *expected* them to be closed circuit, and to open
on overtemperature (like the safety protection on tumble dryer heaters)
but does anyone know for sure? I'll go and test them anyway.

I have it sussed, the open circuit one closes when it is warmed, the
closed circuit one opens. The first one must turn on the fan, the second
one is the "fire" protection. I think I will wire a neon to the second
to see if that is why I am having problems. I wonder if I have an
insulation problem and that this trip is getting too hot, too soon.

Cabinet overheat stats often get too sensitive when the connectors
on them start self-heating due to increasing connector resistance -
they usually carry the full element current.
This might be obvious if the wire insulation near the connector has
deteriorated. Sliding the connector off and back on can help. If the
connector pulls off easily, closing it slightly with pliers to make
it a more firm connection can help.

The other way they can fail is that the crimp connection between the
connector and the wire starts going high resistance. Seen this on
many Smeg ovens across the whole wiring loom.

The stat can also self-heat internally if the stat switch contact
starts increasing resistance. That needs a new stat.

Thanks, excellent point. One of the connectors insulating sleeves has
gone slightly dark and brittle, I will measure the internal resistance
more carefully tomorrow. Waiting for eSpares to deliver a new element
tomorrow, if the stat looks toasted I might short it out temporarily.
Fortunately it is readily accessible with only the back panel to come
off. Unlike the bottom element which was quite a pig.