My hot water starts with full pressure then quickly reduces flow to trickle at all household faucets. Already flushed water heater twice. Flow comes back temporarily once tank refills, then peters out again. No muck or discoloration in water. Cold water side has full pressure (even when Hot water tap is turned on) at all faucets. Plumber was in 2 days ago and replaced hot water line and valve under kitchen sink. He DID shut off water to entire house while making repair.

Hi Glwollitz:

My first guess here is that there is something... sediment from the main supply... that got disturbed and has plugged up the shutoff going INTO the water heater.

Turn the cold water shutoff going into the water heater OFF, then open it up fully again... see if that fixes it. You may need to tighten the packing nut a 1/4 turn if water starts to leak at the handle after you open/close the valve.

Start here... let me know what you find.

MARK

Thanks MassPlumber2008. I have already done this when draining and refilling tank. The valve did leak and I did have to tighten the nut


Once I turn off the hot water faucet, if I allow it to sit about 5min pressure will come back for about 10 sec before flow diminishes again.

Then, next, I would start by removing the old shutoff and replacing it. While the shutoff is out, you should also look down into the NIPPLES of the water heater. These nipples can become clogged over time and can get choked down to next to nothing over time.

They make a solderless shutoff... see image... that can be installed as long as you are 18" away from the heater (if gas). This is called a sharkbite (or gator grip) type of shutoff. Here, just cut out the old shutoff using a tubing cutter and then PUSH fit the new shutoff onto the pipe ends. Be sure to seat deep.

Don't foget to check the nipples... most likely this will be good time to remove/replace as well...

Let me know if you need more...

MARK

One other thing I have noticed is that my cold water inlet pipe is as HOT to the touch as my hot water line going out

If you don't have heat trap nipples in the heater then that can be normal to a point. It is a heating device, so not unusual for the cold water pipe to be warm/hot for 12-24".

The heat trap nipples look like the image below... usually have the INDENT in the nipple.

My guess is that the shutoff is clogged... any chance it is a shutoff similar to the one posted below? If so, before replacing it, see if you can use two wrenches/pliers to disassemble the shutoff valve (unscrews counterclockwise). Then, pulse the water main on/off without the guts from the cold water shutoff in place, reassemble (wrap teflon around threads) and see if that resolved this.

If not, the nipples are next in line for replacement...

Hi, I am no expert- simple farm boy from Missouri. I read several question and answers about this low pressure on the hot side problem as I had it today. Same problem as above, low hot water flow/pressure even lower if you turn on two hot water outlets. I took off the thermoplastic nipple (heat trap nipple above) on the hot side coming out of the top of the water heater. The old Nipple seemed to be plugged up with the little ball that prevents hot water from migrating into the system when not needed. Anyway once I put in a 4" straight nipple (hardware store did not have the 1" heat trap nipple- I'll get one from plumber supply shop tomorrow) I just put on a regular 1" nipple to test my theory on the old one being the problem.
10 minutes later after putting pipe dope on the new nipple treads and tightening it down and reattaching the coupling to the hot water pipe to the house it worked great, plenty of hot water, lots of pressure and flow to all hot water facets at the same time. No leaks. Plumber I talked to wanted $175 for the first hour of trouble shooting, save some cash so far. Hope this helps.
Semper Fi, Col Monte

PS: I had already tried the cold water shut off valve coming into the tank. Took all of the cold water input side off, sweated joints out and checked the gate valve shut off going into the hot water tank. Shut off was clear as a whistle and worked just as advertised, no problem on that side. It was a lot of work getting it all apart and back together as it was a jig saw puzzle of expansion tank, shut off valve, PVC line in, copper line to the nipple etc etc. But eliminated that side and the shut off valve which seems to be the default answer for the problem. I further suspected the cold water side being clogged as the expansion tank had failed and leaked all over the basement last week and there was corrosion going down into the pipes, so thought the corrosion from the expansion tank (only 5 years old) going bad had contributed to the problem. Probably two separate events closely linked in time. Pressure had been going down for a while and we just did not notice it.
Sorry for the double post, thought I had better give the rest of the afternoons activities leading up to hot side discovery.
Semper Fi, Col Monte