Problems with my 'new' deck oven

Hi folks

The Duke convection oven I've been using for the last year broke a week ago. I've used it as an opportunity to 'upgrade' to a deck oven, which would allow me to make more of a hearth style bread and also have pastries etc on a different temp in the other deck... just what I need for my new bakery. I bought a Doyon 3 tray 2 deck electric oven, mainly because the guy confirmed that it was set up for single phase and I could get it before the weekend so I wouldnät miss another farmers market. It's a couple of decades old but ten thousand dollars or so cheaper than a modern equivalent. I wired it in, changed the fuses and was ready to go, doing my first bake in it this morning. I hit a few problems that I'm hoping you guys could help me with...

The first is the huge temperature drop when I open the doors to load the bread. It falls from 450F to about 300F where it stays for what seems like hours. My breads used to bake between 28-32 minutes at 400F in the old convection but they were in for about an hour and a half before they were done. In the top oven at least - the lower oven burnt the bottom of the loaves before the tops were coloured. So the top oven is too cold to bake bread and the bottom is too hot. And I won't even tell you what it did to my scones, suffice to say they were more like pancakes as the needle didn't budge from 300F for the whole time they were in there. Bearing in mind that as soon as I open the door the temperature drops to 300F and hangs about there for... I don't know, an hour or so before it creeps up to 310F and is suddenly on 475F. Day 1 with my new toy tool has taught me that it's a right pain in the arse.

To muddy the waters more the thermostats all have vastly different characteristics. There are three dials. There are only two knobs though, so I slide the one off the middle one when I want to set the lower one. The top dial goes up to 550F (but doesn't look 'original' to the machine), the middle one goes to 450F and the bottom one is comparatively stiff and appears to be at 400-475F where the dial (which I removed from the middle one) is at 250F.

I thought it would be easy to just dial the knobs up and mark the temperatures on them myself according to what the oven thermometer reported, but I  wasn't lucky enough to have two readings the same. 

There is a sticker on the oven that says 'set all thermostats to 375F one hour before you are ready to bake', and another that says 'push all pans to the back of the oven'. Doing so gets the top oven up to about 300F and the bottom to, well, my oven thermometer only goes up to 500F and the needle was off the dial.

Oh, something has just occurred to me. How can I have three thermostat dials but I can only see two thermostats? There are three racks of elements... could one thermostat sensor be wired to two dials? Plus there's a hole where a dial used to be... I assumed this was for a timer as the oven has no timer on it but could someone have pinched a thermostat and bodged it? The same person I suspect that wrapped a cigarette foil around the fuse?

From googling and reading this fine forum I think I have two problems - one is that my thermostat(s) are out and two there isn't enough thermal mass to restore oven temp once I pop my 20-loaves of bread in each deck. Is there any point in me heading down to home depot and buying some unglazed tiles or should I accept that my oven will never do what I want it to and go back to the convection one while I save for a newer deck oven? 

Re the thermal mass the 'deck' parts are about 1/8" steel plate, which I can lift up to reveal the elements. If I went and bought some tiles would I just lay them on these, or should I glue them onto the plate and grout them etc? 

Once you've helped me with this can of worms I'll post a new thread on the best way to bodge a milk steamer from an espresso machine into the oven to get some red hot steamy action going on in there.

Jamie