Display Solr search form on every pages
I managed to work this one out, to get the block ready to be displayed I used preproccess_region (see code below)

function THEMENAME_preprocess_region(&amp;$variables){
    $site_search_block = module_invoke('search', 'block_view', 'search');
    $variables["site_search_block"] = render($site_search_block);
}


Then in in my region .tpl file (region--menu.tpl.php for me) I put the following code to display it.

&lt;?php if($site_search_block){ print $site_search_block; } ?&gt;


As an additional bit of information if you want to edit the output of the form as I did, although I didn't ask about it here, this function should help you:

function THEMENAME_form_search_block_form_alter(&amp;$form, &amp;$form_state, $form_id) {
    $form['#id'] = 'siteSearchForm'; //Set form element ID

    //The form elements (I think)
    $form['search_block_form']['#title'] = t('Search'); // Change the text on the label element
    $form['search_block_form']['#title_display'] = 'invisible'; // Toggle label visibilty
    $form['search_block_form']['#size'] = 10;  // define size of the textfield
    //$form['search_block_form']['#default_value'] = t('SEARCH'); // Set a default value for the textfield

    //Submit button element values
    $form['actions']['submit']['#value'] = t('GO!'); // Change the text on the submit button
    $form['actions']['submit'] = array('#type' =&gt; 'image_button', '#src' =&gt; base_path() . path_to_theme() . '/img/search-icn.png');

    //Add extra attributes to the text box
    //$form['search_block_form']['#attributes']['onblur'] = "if (this.value == '') {this.value = 'SEARCH';}";
    //$form['search_block_form']['#attributes']['onfocus'] = "if (this.value == 'SEARCH') {this.value = '';}";

    //Prevent user from searching the default text
    //$form['#attributes']['onsubmit'] = "if(this.search_block_form.value=='SEARCH'){ alert('Please enter a search'); return false; }";

    //HTML5 placeholder attribute instead of using the javascript
    $form['search_block_form']['#attributes']['placeholder'] = t('SEARCH');
}