No hot water at any faucet?
No water whether hot or cold at faucets?
Do you have 3 shut-off valves on water heater......no check valve.
Only 1 or 2 valves on water heater.....then outlet would have a check valve.
No water on hot side of faucets...then check valve is either plugged OR has failed.
The check valve is right at water heater tank......you can remove internals to get hot water flowing and replace when convenient OR leave it out.
Only really needed IF you winterize.
I prefer the 3 shut off valves (hot/cold/bypass)....no check valves that fail.