Some samovars have a special floating device near the heater, which turns the latter off, if the water in the tank does not engulf the spiral entirely. This design, however, did not prove very popular, since it has an additional moving part, which, in turn, constitutes yet another point of failure. Thus, it caused more problems than it solved, so Russians chose to look after the simpler samovars. Generally, Russian technology assumes dumb machines and smart humans, not the other way around.

Don't complain about the missing switch -- just pull the plug, if you want to turn the heating off; the only moving part in a samovar should be the valve of the faucet.