Cointra Flues. Replacing your Morco Water heater with a Cointra CPA 6 or Cointra CPA11. So You have a Morco EUP 6 with a 90mm flue pipe. You will need a new flue. For a Cointra CAP 6 a 100mm & a Cointra CPA 11 110mm. Your Gas Safe Engineer will advise you.