What the expected temperature veration between shelfs in a fan oven?

[Lower]

I can see it getting red hot, and the oven "heating light" next to the knob does go out and then back on as expected. Nearly always when elements fail, they totally fail.

Some of them are twin coil.

 

[foxhole]

I had the door closed, putting the stat on each shelf in turn, waiting about 15 minutes before reading it. I repeated this 2 times to check I was getting readings I trusted.

On my oven at home, on the middle shelf, the stat read about 20c over what I have the oven set to.

Oven stats are not completely accurate and temp varies continually .

 

[jj4091]

Not a problem I've ever investigated but a couple of observations:
The instructions on food packaging usually says "cooking instructions are a guide only".
Have you checked the door seal is ok?
I would have thought the thermostat on the oven is failing if it is an old oven.

 

[JohnD]

That's an idea

Maybe the door or seal is damaged and cold air is entering, perhaps at the bottom.

Or maybe a vent from the hot fan is obstructed

 

[ringi2]

I would have thought the thermostat on the oven is failing if it is an old oven

That was my first thought, hence I replaced the thermostat. When that did not work I started to measure the temperature. I will check the door seals the next time I am in the property.