Typically it is the hot outlet check valve (top fitting/line) that is plugging up.
The check valves are cheapo plastic junk that falls apart or clogs up.
With water off and pressure relieved you can remove the line then unscrew fitting on tank. You can replace with a nipple and install a shutoff valve vs installing another check valve.
No more faulty check valve just use the new shutoff valve when you bypass water heater for winterizing.
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31