Try curl fallback.

scraper.rb

@@ -1,9 +1,19 @@
-require 'scraperwiki'
 require 'mechanize'
-
-agent = Mechanize.new
-
-page = agent.get('https://www.fastenergy.at/heizoelpreis-tendenz.htm')
+require 'scraperwiki'
+require 'open3'
+
+url = 'https://www.fastenergy.at/heizoelpreis-tendenz.htm'
+
+page = begin
+  agent = Mechanize.new
+  agent.get(url)
+rescue
+  out, err, status = Open3.capture3('curl', '-kL', url)
+  puts out
+  puts
+  raise err unless status.success?
+  Mechanize::Page::new(URI(url), nil, out, nil, agent)
+end
 
 rows = page.search('#tabelle tbody tr')