selling - home inspection came back - water

[George P.]

The buyers are asking for the required expansion tank on the (gas) water heater to be installed. The unit was installed appx 3 years ago by the licensed plumber.

So I have googled and came across this page where it states: 

"The International Residential Code (P2903.4.2) requires the installation of an expansion tank on a hot water tank where thermal expansion may cause an increase in pressure. The tank is only required when the water supply system incorporates a backflow prevention device, check valve or similar device. Similar language can be found in the Uniform Plumbing Code under section 608.3."

Here is our heater's fact sheet and I don't see any of these devices.

Any help is appreciated!!!

Thanks!!!

P.S. Also, on a side note, we bought another property 3 months ago, with newer electric water heater w/o an expansion tank, and our inspector didn't make a not of it. So I am thinking one of the inspectors is wrong.