Hello I currently own a mk6 Ford Fiesta ztech s 1.6 I have got a glow plug circuit a malfunction been told it could be a fault with the ecu I have tried to replace anything yet is there any suggestions on what the cause could be

With engine ignition off, locate the glow plug relay. Its in a small square black plastic box next to the car battery if you have the car i'm thinking of. Pull the glow plug relay out and give it a tap or two with a screwdriver or similar then carefully sand down and clean the metal pins/connectors of the glow plug relay. Push it back in but hold the bottom of the black box to support the push down force you apply to avoid breaking the box. Push down other relays in the same black box to make sure they are secure too. This may not fix the issue so treat it like an elimination process if it doesnt. It might be worth trying another working relay or get the one you have checked out. 

Mine went into limp mode due to this. Mechanics couldn't fix it because error codes did not make sense. I figured it out myself. This was a few years ago and i didnt even change the glow plug relay, i just cleaned it as above and car is still running fine up to now and fault never came back.