Is it a game breaking house rule, if all in combat healing source heals the rollable maximum?

In the next week I will start a new campaign where I will be the DM. The players will be totally new to the DnD World, and because of that, I want to let them to freely choose the class and race which they want to play, but it seems like there will be no healer PC, just damage dealers and some kind of PC which maybe will have some healing.

I want to play with them in a relatively long campaign (I’m planning from level 1 to 20) and because of that, I really want to give them more opportunity to overcome the missing healing power. Will it break anything, if I let the semi-healer PC to heal the maximum roll-able number with any healing skill, which he/she uses in combat? For short rest I wouldn’t allow this house rule, so I really want to know, if it would be too powerful in combat house rule or not, and why?