Bosch HES255U Covection bake slow to get up to temp.

f resetting the high temp limit switches did not resolve the issue, it may be a problem with the broiler and bake elements themselves or with the wiring and connections that supply power to them. It would be best to have a qualified technician inspect and diagnose the issue to determine the necessary repairs.

your correct the only difference between a regular oven and a convection oven is that it has a fan.when you open the oven door the fan should be spinning to a stop if this is not the case you may have a problem with the fan.

Possibly a bad oven temp sensor. If the uinit doesnt read a temperature it will shut down to prevent a fire or over heating. The temp sensor is a thermister A temperature variable resistor that changes value as the temp changes. so If the main board doesnt get a response within a vertain resistance range it shuts things down. Sometimes since those parts are in the actual cooking area and subject to the heat and steam from cooking they can rust and break, or just get old and break. Or slam the door and break, you get the idea!!

I will say that is the control board that is not working properly. Have you try to unplugged for phew minutes?, this will reset the current settings. If not, I will star replacing the control board. Good Luck!.

is this 400c or 400f

Most likely the problem is your bake element. When the oven is preheating it uses both the bake and the broil element. When it's done preheating it uses only the bake element, so the broil element is heating it up, and since the bake element is not working the temperature drops until it starts preheating again.

If you are monitoring the oven temperature with an analog style thermometer you may actually be ok, but seeing the thermometers slow reaction time.
Some newer ovens actually do pre-heat beep prior to reaching temp in an effort to conserve eelectricity.
A good home test is to try your oven at several different temps to see if there is any variation in internal temperature. Try it one day on 300, the next at 375 and another day at 450. Give your analog style thermometer time to catch up (usually just about 15 min) and leave it on for a half an hour to see if the temp maintains.
Also Beware of aluminum foil AND THE NEW OVEN LINER MATS as they can alter oven performance bay absorbing and blocking the ovens natural heat radiation and convection air flow currents that happen in all ovens, not just convection models.
Another interesting fact is that older ovens used a thermostat in them that operated much like your thermometer and was very slow to react making the oven typically about 100 degrees hotter than where the customer set it. This was just a fact of life before the advent of electronic temperature management and became noticeable when people began trying to bake older "hand me down" recipes in the newer ovens with less than stellar results.
You can mimic the older oven performance by preheating the oven about a hundred degrees higher than called for and after it reaches temp, re-set it to the correct temperature and put the items in right away.
If you find your temperatures fluctuating ask your servicer to replace first the temp sensor and as a last resort the control board as this part is usually pretty expensive.
Good Luck with this!

We have the owner's manual and have uploaded it to our site for you here.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

WHAT WAS HAPPENING AT 1ST YOUR HI-LIMIT TERMAL SAFETY OR OVEN TEMP SENSOR FELT THAT THE OVEN WAS GET TOO HOT AND SEIZING OPERATION UNTIL SAFE TEMP WERE OBTAINED THIS IS GENERALLY A FAULTY OVEN TEMP SENSOR. I WOULD ADVISE YOU TO CONTACT A CERTIFIED TECH TO LOOK AT IT AND P.S. DON'T MENTION THAT YOU TOOK THE MACHINE APART MOST SERVICE COMPANIES WILL NOT SERVICE THE MACHINE IF IT BEEN TAMPER WITH BY THE CUSTOMER DUE TO INSURANCE AND LIABILITIES

If you need further help, reach me via phone at https://www.6ya.com/expert/marlon_56d9a24f02585258

I have just checked the baking guide in the manual and have found that it may not be us after all. (Maybe this is why they telll us to read the whole manual. Well, I never have) According to the cooking time for Baking, the range is very extensive. For example, an angel cake at 350 could take from 28-50 minutes, buscuits at 375-400 could take 8-16 minutes, layer cakes at 350-375 could take 25-40 minutes, pound cakes at 325-350 could take 45-70 minutes and fresh pies at 400-450 could take 35-60 minutes. Basically, the baking directions on the box means absolutely nothing to use Amana oven owners. We have no choice but to cook our food or baked goods until they are cooked, whenever that may be. :) Linda