I make a good living repairing combis. I have an open vented hot water cylinder at home and a regular boiler. You couldn't get me to put a combi in to replace that if you gave it me. I would actually think you were mad. If you offered as a means of filling a bath quickly another combi I would call for the men in white coats.

Thank goodness combis are so popular, I'm guaranteed work for many years to come.

Thank goodness I have enough intelligence to learn from other peoples mistakes and kept my airing cupboard.