Gas/Propane heater, I don't think it's the well as the water tastes fine and we only smell it via hot water. We noticed it in the shower first, but I checked the faucets. No smell in cold water, in fact no smell in hot before the hot actually gets there.

There's a holding tank, but its between the heater and the well.

The heater is actually on a platform, so very little space above it, about 24 inches, I will probably reach out to a plumber, since short of cutting the existing one as it comes out, I don't see a way to get it out.

thanks again for all the options/info, this is new to me, so learning and will be reaching out to the rental manager to pass along to the landlord.

Thanks again! any other advice, keep it coming!