I have a convection oven that has been working perfect for two years. Triphase electrical. Work with spongy cake. Recently, couple of my cakes after baking, have been sinking, the top sinks and the bottom is very dense. 

I am using same settings, temperature, time, baking mix, baking pans. From the same rack, one sinks the other does not. ??????

With extra thermometers measured the temperature, variation is not over 10 degrees

Could it be the variation of tri-phase power in the building or should I call technician to service the oven?

In the meantime, should I raise the temperature 25 degrees to help my baking?

Thank you, I am very anxious with this issue..

I had this same thing happen to me about a month ago. What recipe are you using? I was using a WASC recipe which is a modified/extender boxed cake mix recipe. When the recipe was first posted, the boxed mix quantity was more. Duncan Hines, Better Crocker etc have since reduced the amount of cake mix in each box, therefore, the WASC recipe I was using was no longer working properly. The weird thing about his is that I have not had a problem with Duncan Hines, it only happens when I was using Betty Crocker chocolate...the vanilla was fine. If you are using the WASC recipe, maybe this is your issue??

HTH

I am the poster of the *original* WASC recipe.  I almost alwyas use BC mixes.  I seldom bake anymore but the few times I have I use a 9x12x2 pan (Magic Line) and the recipe *exactly* as posted and it comes out perfectly.  I have used Butter Pecan, Lemon, white and chocolate mixes so far.  I have increased the temp because I have a different stove that seems to not be accurate (don't have a thermometer). 

When you say it sinks can you be more specific or post a picture??  That would help alot :)

Is the sink hole small - like dime or nickle size or is it a major thing that is deep?

Usually if I ever had a small depression/hole I really didn't mine as it was easily covered with icing.  If it more along the major lines, then we have to try to figure out what might be the problem.\

If you are using a mix, it could be that - they can be old, or much more frequently than you want to think, a slight burb in the creation of the mix can cause major baking problems for us.  When I was baking I often had to call the company who would deny there was any problem only to find by taliking to friends and other bakers it just had to be the answer.  Come on, a dozen different people in all different parts of the US can't just happen  to mix up batter wrong! (which is what the mix company tried to say).   

AThank you, Kakelady, actually I made all of my cakes from scratch. I called the oven technician and he found one of the three heater elements was malfunctioning I just have to wait for the spear part and will be back up and running.