Fender Bassman 1200 - Fan hasn't kicked on yet!

Just curious if anybody has used this head before and might know anything about it?

The head has a fan in the back. I noticed in the shop that it didn't kick in. The salesman told me it was because it doesn't kick in until the amp starts to get hot. Obviously I didn't turn it up loud enough in the shop to get it hot.

Several months later, the fan has still never kicked in. After a few practices with my band, it got pretty hot, but still no fan.

I will confess I am new to the world of good gear. Up to this point I have only ever owned practice amps, and am just not used to having a head that heats up. I am just worried that this may not be normal and I definately do not want it to overheat.

Any advice? Anybody ever heard of this before? Do you think the salesman was just trying to get his commission?