Is their a way to reset all default settings in theme customizer?

To delete your option use the delete_option() function. More explanation below. 😉

If it’s your own theme then I believe you should be saving your option changes via

http://codex.wordpress.org/Function_Reference/update_option

which you can read via

http://codex.wordpress.org/Function_Reference/get_option

And if you want to delete your option

http://codex.wordpress.org/Function_Reference/delete_option

Have the default settings in your code. That way you test if the option does not exist rather than needlessly creating an option you just check if the option is set. If it’s not then use the defaults.

There’s some really good theme documentation available but I am behind in my reading. I alway find the wrong ones so I’m going to see if this works:

*Paging Chip Bennett! Obligatory Child Theme reference here!*

Inside joke and if I find those links I’ll post them here. 😉

To the best of my knowledge there is no global reset. I have to ask what way are you registering your settings? Default way which is handled by using: theme_mod or options API? If you are using theme_mod one way I can think of would be creating a reset settings button.

So it would be something like:

// Removes all theme mods
remove_theme_mods();

// If we haven't already declared them, declare some default settings
$defaults = array(
	'links' => 'ddd',
	'link_hover' => 'aaa',
	'headers' => 'fadccd'
	);

// Re-create all the default settings.
foreach ($defaults as $key => $value) {
	$wp_customize->add_setting( $key , array( 'default' => $value ) );
}

Keep in mind that is the default way that WordPress handles that and you could potentially use the options API by adding 'type' => 'option' to the array.