I'll just add that if you decide to replace the unit, you may want to check if any codes have changed since the prior installation was performed. It most cases, the changes are much easier to perform during the replacement as compared to once the unit is installed or further down the road if an inspection (e.g. home sale) reveals a deficiency.

Here is what I used to retrofit my two homes. Simple and easy to install.

https://www.rinnai.us/residential/tankless-water-heaters