MORCO Replacement Water Heaters
Morco Products have discontinued several water heaters
MORCO REPLACMENT WATER HEATERS & BOILERS
Which Cointra CPA to replace your Discontinued Morco Water Heater
MORCO Replacement Advice
So for flues if you are unsure measure the flue you have, just because its there does not mean its right. Incorrect flues will restrict the performance of the unit. Your installing Gas Safe engineer will do this for you.
You cant have a smaller size flue for a bigger unit so if you have a 100mm unit you cant fit 90mm flue. You can go the other way thought. So you could have a 100mm water heater and a 110mm flue. With an adaptor.