Very Weak Water Pressure On Hot Water Side,Tankless Heater Not Turning On

[Mugsysiegel]

So today the wife was doing dishes and the hot water worked fine. As I came in the door she said the water pressure for the hot side is very weak and cold now. I go out back the hot water heater is not venting exhaust at all. So I go back inside the water is barely trickling on the hot side. I checked water pressure on regulator on hose it’s fine and the cold water side has lots of pressure. The hot water side is barely a trickle. I go out and remove the small water inlet filter on the Furrion water heater and clean it off,it was hardly dirty. I reinstall. Try to fire it up and nada. I’m at a loss what can I try? It has not been below 55 degrees so no freeze.

[Najataagihe]

Check the bathroom hot water faucets to see if there is a kink/blockage between the bath and the kitchen.

If they are fine, the problem is between the bath and the kitchen. I would check under the sink and make sure nothing is kinking the hose, before ripping things apart.

I would then take the sink valve off and make sure you were getting water to it.


If you have no flow in the bath, go outside and drain the tank in an attempt to relieve the pressure on any blockage, hoping it falls out of the way.

Then, trip the water pressure safety valve and see if the heater is getting water in it. I would pressurize the system, turn OFF the water, then trip the valve. This will let you know if it is working without putting a lot of stress on the system or fling water everywhere.


After that, I would suspect you have something blocking the pipes.

The only way to troubleshoot that is to start where you have pressure and start taking fittings apart, until you find the one that has no pressure.

The blockage will be just before that one.


This is where a trombone snake comes in handy!

I cut the brushes off one of mine and use it to run up supply pipes to ream out any lime build-up.

Works like a charm.


Good luck and let us know what you find!

[Najataagihe]

This is weird!

Your reply doesn’t show in the forum, but showed up in my email!


Here is the message that has just been posted:
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So the cold water has great pressure and the heat controller in bathroom never says flame now either. Could it just be a clog in the small copper lines in tankless heater? Is that what you refer to snaking out?
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The controller will never fire up the burner, if water is not flowing, so that is no worry.


The snake is a last resort for the main supply plumbing, but it is small enough to snake the thin copper tubing, as well.


Believe me, the LAST thing you want to do is start taking the piping apart, but that may be the only way to get rid of a blockage.


The cold water supply and the hot water supply are two totally different sets of piping, once the cold water supply hits the water heater.


You didn’t say if you have an external filter on your supply hose.

If not (Heaven forbid, it’s that important), you may have detritus right where the water enters the water heater.

If that was the case, though, I would have expected you to find it, when you cleaned the screen.

To double-check, turn the water off, take out the screen filter and turn the water on for a quick blast and see if it blows junk out the screen opening.

[Mugsysiegel]

I have a filter on the hose and when I turned water on with filter off on water heater nothing notable came out. Could I just use a pump and pump say 6 gallons of vinegar into the system and leave it in lines/water heater etc for all day? I can’t see a way in my 2021 340 rds to get behind the water heater from the basement. I could always run clean water for an hour with faucets open after it soaked.

[Riverbug]

You've verified there is no flow to any of the faucets on the hot side? Have you checked the bypass valve to see that it is in the correct position? Perhaps that would be a good place to remove the outflow water line connection and see if you get flow directly from the water heater. If so, you know it downstream of that. I would do this without the heater turned on. You just need flow, not hot water at this point.

[Mugsysiegel]

You've verified there is no flow to any of the faucets on the hot side? Have you checked the bypass valve to see that it is in the correct position? Perhaps that would be a good place to remove the outflow water line connection and see if you get flow directly from the water heater. If so, you know it downstream of that. I would do this without the heater turned on. You just need flow, not hot water at this point.

There is flow just about 1/3 of normal flow on hot side. I have verified the nautilus panel is correct and if I turn the red one 90 degrees cold water comes out the hot side at full pressure so it must be in water heater id think. Could I do the flush I referenced above?

[trailrydr]

Maybe sediment in tank.... would focus on connections in/out there. Probably start by draining tank and checking for debri. Could even place some city water pressure while draining to maybe dislodge any debris in tank too. A back flush may also help remove any outlet debri out the drain if you can get a hose on it there.

[Riverbug]

There is flow just about 1/3 of normal flow on hot side. I have verified the nautilus panel is correct and if I turn the red one 90 degrees cold water comes out the hot side at full pressure so it must be in water heater id think. Could I do the flush I referenced above?

I wouldn't certainly think that would be the best method at this point. I've know that for my portable on demand water heater it suggests that you circulate vinegar through the system using a 5 gallon bucket and a couple of gallons of vinegar. I've only done it once so far using a stand alone 12v pump and it did get pretty dark by the time I was done.

[RVing in Michigan]

So today the wife was doing dishes and the hot water worked fine. As I came in the door she said the water pressure for the hot side is very weak and cold now. I go out back the hot water heater is not venting exhaust at all. So I go back inside the water is barely trickling on the hot side. I checked water pressure on regulator on hose it’s fine and the cold water side has lots of pressure. The hot water side is barely a trickle. I go out and remove the small water inlet filter on the Furrion water heater and clean it off,it was hardly dirty. I reinstall. Try to fire it up and nada. I’m at a loss what can I try? It has not been below 55 degrees so no freeze.

I just had this same issue two weeks ago. No volume out any hot water faucets. I have a drain valve on my water heater so I opened the ball valve and hot water shot out as expected. I looked through my window in the basement that lets me see in the utility area- no issue visible and no kinked lines. I then knew what to look at. Sure enough, the check valve on the water heater outlet has a plastic piston with a spring and a retaining clip inside the valve. The clip had fallen off and it and the spring were missing. (obviously setting in the bottom of my heater tank) When this happened, the plastic piston gets pushed out of the check valve (with water flow) and then blocks the connector fitting. I could duplicate this event by shutting off the RV water supply, then open my tank drain to shift the piston back, then Turn the water back on. Then i turned on the hot water faucet VERY slowly and the flow was back. Put in a new check vave and all is well.

https://www.amazon.com/dp/B00HJ6P0Z8...roduct_details

[Viper02]

might check this valve and make sure its set correctly