[ekeZ]

2 story flat---Why does my water hot water in my kitchen and bath on 2nd level cut off when my 1st floor unit turns their hot water on?

[massplumber2008]

Hi ekeZ:

Most likely, the issue will be related to the VOLUME of water available to your home at any one time.

Tell me, is the water main 1/2" feeding into the home? Are there two different water heaters? If so, are both water heaters fed from a single 1/2" copper water pipe?

If so, then when someone opens a hot water faucet upstairs and then downstairs water volume will certainly drop off as the 1/2" water main tries to fill two 1/2" water pipes into 2 different heaters.

Further, when volume drops off like this you can be sure GRAVITY isn't working to your benefit either. Simply put, when volume drops off like this water will seek the easiest route to flow, i.e. water will flow out the lower pipes easier and the result will be less water to upstairs.

Answer my questions... maybe I can pin this down to something else. Otherwise, most likely the only way to fix this is to increase the size of the water main from 1/2" to 3/4" at least up to and including the cold water feeds into the water heaters.

Finally, most water mains come into the home 3/4" but lots of them get reduced to 1/2" right after the meter. Wonder if that is your case? Let me know as much as you can.

MARK