... house started fluctuating hot warm cold. Both hot and cold faucets do this now. I suspect that when the valve is fixed all will return to normal?

I could help you better if you can give more details. Was any work being donbe or anything replaced?

What type / brand / model faucet is it ? With majority of faucets, the up-side-down installed faucet should not cross-contaminate hot water. What other work was done in the house ?

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Milo