Rinnai Tankless Water Heater Will Not Flush

deblaw10

I have owned a Rinnai Tankless water heater for over 10 years. I flush the unit quarterly with vinegar. I have tried to flush the unit several times over the past few weeks and have been unsuccessful. The pump is working, but the unit is acting like the valves are closed. I have never experienced this before.

I spoke with Rinnai and they told me my transfer pump was too powerful. The one I was using was transfering at 25 gallons per minute. I needed one that pumped 3-5 gallons per minute. I found a garden pump and tried, I was unsuccessful. Called Rinnai again and they said my pump isn't powerful enough. I asked for a recommendation for a pump, they do not give recommendations. I went back to my old pump and attempted to pump the unit again with Rinnai suggesting to turn my hot water on and shut the water off from the tank instead of the faucet. This will keep the valve open. This was also unsuccessful. Any ideas why the unit is not flushing?

nibs

No suggestions about why, but if you can get your hands on a 12V RV water pump (Around $40 new), try using it they put out about 3gpm at up to 40 psi. If you were near, I would give or lend a used one that you could use.

deblaw10

nibs

Thank you! I did purchase a 3gpm pump, but I was told by Rinnai after I purchased that it needs 18foot head. Those are hard to come by this time of year. I don't understand why the pump type I have been using for the past 11 years suddenly doesn't work.

Leon82

Could the impeller be worn?

deblaw10

Leon82

I have tried 3 different pumps, all work fine until they are hooked up to the water heater. It's like the valve is closed, but it isn't.

Leon82

Inlet screen clogged?

deblaw10

Leon82

No, the inlet screen is clear of debris.

Larry Weingarten

Hello, A trick I've used to unclog plumbing is to reverse flow, repeatedly. That way if there is sediment plugging things up, it will eventually get worked loose. I don't know if you have a check valve in there someplace; if so this idea wouldn't work. Still it seems it couldn't hurt to try.

Yours, Larry

deblaw10

Larry,

I have tried to reverse the flow, but no luck, however, I did not try several times. I have never had this problem before, like I said, I flush my unit quarterly due to having very hard water.

bobn4907

so how did you resolve your issue; I believe I have the same problem

Dekito

I have rhe same problem ,done many times now its not working 

Intplm.

Has anyone called Rinnai customer tech support?
1-800-621-9419.
What did they suggest doing?

f0x14

I had this problem twice, tried reversing the flow and that fried my control board. 

What I got to work just now was with the unit on and having one washer hook up hose that’s about 3/8” in diameter inside as the feed and one thats about 1/2” inside diameter as the discharge. The pump is also a sump pump that pumps 1980 gph 1/4 horsepower so yes definitely overkill but the hoses setup the way I did helped resolve this issue apparently regardless. 

hot_rod

Does water flow through from your homes water system? Then a pump should flow through it as it has in the past

its psi not gpm that you need, those sump pumps only pump about 15 psi, so you may need a bit more.

If the heater operates with 20 psi of water pressure, you need a pump that supplies that.

You are sure the hose isn’t clogged🥴

pedmec

they sell kits for just this purpose. comes with pump and descaling solution


https://www.jcwhitlam.com/Product/1/114/102#

mahonri11

I was having this same issue and got it working by doing the following. 1)first reset the code to resume normal function. Press on/off button 5 times for my model. That turns the unit back on for 70 hrs and blinks the set temp and lc code. 2)unplug the water heater, shut off the gas valve, close inflow and outflow water valves. 3) connect hot/cold lines to the respective in/out purge ports and open both in/out purge valves. 4) connect cold input line to the sump pump, put it in the solution bucket 5) put your output line in the basket to complete the loop. 6)Plug in the water heater with the gas valve still off. This will prevent the heater from heating up and turning on completely but will allow the heater to open an internal valve (you should hear the system opening the internal valve) that will allow the solution to flow through the heat exchange. After hearing the system open the valve 7) Plug in the sump pump, solution will start flowing immediately through the system. Hope this works for others as it worked for me. Good luck!

uofs76

Thank you! That solved my problem. After trying about 30 variations, the vinegar solution always slowed to a trickle after 30 seconds. Based on your info, I did the exact same setup but I left the electricity to the heater on for the first 30 seconds of the flush. When all looked good I turned the heater off and the flow continued to be strong. Very happy I read your post.

KMB

I have researched the sump pump for the tankless water heater flush, and Rinnai recommends that the pressure be set at 1/6 hp instead of 1/4 hp.

https://www.rinnai.us/residential/flushing-my-rinnai-tankless-water-heater

Intplm.

Since the original post I have researched and used this numerous times.