I'm not familiar with the oven and couldn't find instructions in english. Many of these ovens have the option to run as a normal conventional oven or in "convection" mode. Are you running your oven in convection mode (ie. the fan is turned on)?
My main concern with the flour is not that of protein content. If your flour is in the range of 11-12% you should be OK. Different flours are designed for their appropriate baking environments. Most if not all all-purpose, bread, or high gluten flours in the US contain small portions of barley malt which aids in coloration/browning especially at lower temperatures (below 700-750F). On the other hand these malted flours tend to burn more easily at higher temperature. Unmalted flours such as Caputo 00 for example are designed for higher temperatures (+750F) and do not brown well at all at lower temperatures such as yours. If you do a search on Caputo 00 and browning you will find several threads discussing inability to brown this particular unmalted flour in a home oven. Scott123 made a rather well explanation of malted/unmalted flours and their browning ability in a recent response that I would encourage you to read http://www.pizzamaking.com/forum/index.php/topic,10024.msg101191.html#msg101191 . Look at the ingredient list on your flour bag, does it list barley malt or diastic malt as an ingredient? Do you have more specific brand information on the flour or the mill it originates?
For your reference, a bag of King Arthur Bread Flour lists the following ingredients: Unbleached hard spring wheat flour, malted barley flour, niacin, reduced iron, thiamin mononitrate, riboflavin, folic acid.
Another thought in regards to browning. It is probably a non-issue with a convectional oven but you could try moving your stone to a higher rack in the oven. Heat will vary at different levels of an oven.
Yesterday I tested some of the options in my ovens, now I finally know how to control the broiler.
Until now, I've been using it in either convectional mode, or one of the broiler modes that hits only the outer coil (there are two on the top) and the bottom coil, which is hidden, and until yesterday, I wasn't aware of its existence.
I'll try moving the stone close to the fan, together with the strategy Scott has suggested, and when I'll get a Raytek thermometer I'll experiment it.
I'm so glad you noticed that the problem might be related to the flour content, and indeed, none of the flours I've been using contained malted barley.
Moreover, I'm not sure any of the standard flours in Israel contain malted barley, but I'll check to be sure of that.
If it's true, I thought about getting one of those: malt powder from a beer supplies store, malted barley to grind with my coffee grind meal, or the last and most tedious option-buy unmalted barley and malt it at home (I found few guides for that).
Do you know how much malted barley is there on King Arthur Flour?
Almog, I've attached a photo of what I believe is your thermostat below.
Being so far back in the oven, I'm not sure it's going to work for the frozen towel technique. You could, in theory, probably take it out of it's holder and set in on a shelf to make it more accessible*, but I'm not sure that's the ideal scenario. I would try some broiling. Move the stone to the second shelf from the top, pre-heat it to 480 (using the convection feature), crack the door and turn the broiler on for a few minutes and see where you can get the stone. If you can hit 550, I think that should do it.
And Sconosciuto is correct about making sure that you're using flour that contains malted barley flour.
*You might also, depending on how much extra wire is there, place the thermostat on a shelf below the stone, allowing you to broil the top of the stone to your hearts content, but, in order for the oven to work for other baking needs, you'd have to return the thermostat to it's bracket after baking pizza.
Thanks! I believe you're right about the thermostat.
Yesterday I tested the temperature with my BBQ thermometr, which can't measure the stone temperature, but since I used it with the oven's door half open and got up to 490f in convectional mode, I believe the stone might hit it much higher.
I'll test it more accurately when I get an IR thermometer.
Hopefully, adding a malted barley to my flour and using better heating strategy will give me good result. Then I'll continue with changing the thermometer's position.