Just fixed two leaking Peerless faucets (two-handles, one spout) in the bathroom and kitchen; in both cases the hot water couldn't be fully shut off. The shutoff valves didn't work, so the house shutoff valve was used. (In the process of finding it I first tried shutting off the HW heater intake pipe valve, but couldn't move it, and started to unscrew a small nut beneath it until water came out, so I stopped.)

With the new stems installed the hot water can be fully shut off, but now there's little hot water coming out of any faucets, including another bathroom faucet that wasn't touched and a shower. I checked to make sure the shutoff valves were fully open. If I wait half an hour or so, I can get a half cup of water, so there is some flow.

Cold water comes out fine at all faucets, and the toilets refill as usual, so it's not a pressure issue.

The HW heater intake is cold, and the outbound pipe is very warm, so something must be restricting the flow near or at the HW heater.

So... do I need a new water heater? Did unscrewing the small nut beneath the valve introduce an air bubble that could be blocking the flow, and if so, is there a was to 'clear' the pipes?

Hi OHO...

So the cold water is fine everywhere,, huh? You said you didn't move that shutoff above the heater... just moved the packing nut... huh? That could mean that the shutoff isn't defective but did get clogged when turning all back on.

You will probably be best to just replace the shutoff with a new ballvalve and be done with this. They sell a sharkbite type of ballvalve that doesn't require any soldering and can be used here as long as you are at least 18" above the water heater... see image. It should be available at all home depot stores.

Here, shut the water main again, drain the pipes, cut out the old shutoff using a tubing cutter, clean the copper lines with sandpaper and then push fit the sharkbite shutoff in place... be sure to seat each end deep enough into the shutoff.

If that fails to fix then you will need to remove the pipe/fittings from the inlet and outlet and see what is clogging the nipples. You DO NOT need another water heater... ;)

Let me know how you are doing as you go along here... glad to help.

MARK

Problem solved! Tried again and managed to budge the HW heater intake valve open and the hot water flow improved. Still plan to replace it since it doesn't close/open completely, though I can't use the ballvalve you suggest as the valve is 12" below the top of the heater.

Thanks for focusing my attention on the key to the problem!