Rinnai tankless hot water - just shuts down after 5-8 minutes

stephenmatlock

This is a brand-new unit, installed by an authorized technician.

If I run it to draw a bath, I get maybe 1/4 of a bathful, then the system shuts off.

A shower runs out of hot water in 5 minutes.

Trying to wash dishes and run the hot water for a rinse, the system shuts down.

The installer came back and found no issues.

It happens about 80% of the time, but not consistently.

I've looked at the troubleshooting manuals, but don't see this issue. It's not a "sandwich" of cold water. The system just shuts off, and never turns back on again.

Solution is to turn off the water, wait 1 minute, and turn it back on, but this is a *brand new system*

Snowmelt

then if he is authorized dealer and he see the problem he should be able to get a new one

lchmb

did you check the water strainer for debris? When the unit shut's off, do not shut the water off..Go to it and see if it is flashing a code. If not have him check the impeller to see if it's blocked as well..

j a_2

The water strainer is on the lower right side of the unit...it's a black knurled quarter sized plug....Often on i seals that were done to replace a failed water heater debris will be in the domestic system....Your ariearors on fixtures will even clog up....Is it sized correctly? Ground water temps are an important variable....Bit surprised your authorized installer is not on this. my need removal to the unauthorized list.....post some pictures....we will know just how authorized he is

j a_2

See if it's a code 11

Jack

You don't list the model! Is it a condensing unit. Is it throwing an error code 25? Look in your manual and you can show the error code history. This is a common problem with improperly installed condensate drain lines. The unit is internally trapped and additional traps will fault the unit out. You can check this yourself by disconnecting the drain line below the unit and let the unit drain into a bucket temporarily.

FrameMaster

Hi Jack, I have the same problem with my RUC90i Rinnai. Just installed a few months ago by a licensed plumber, and I have the same issue. I get a code 25. I just drained the condensate trap drain plug. If it is an improperly installed condensate drain line, how can I correct this? What should I look for that will tell me it is improperly installed?

Jack

Disconnect the drain line at the factory connection at the bottom of the water heater. Run a piece of clear vinyl tubing or pvc to a bucket and let the unit drain into a bucket. Terminate the drain above the lip of the bucket. Report back!

j a_2

To the posters....step back and take a picture of the installation..It really helps in resolving issues....list the model number and amount of hot water fixtures it serves.....If in fact the installer is a so called authorized installer,whatever that means....Why can't he fix it...Also ask the installer if he did a gas pipe sizing chart....They are great units, when they are properly sized and installed....Your local rep should offer technical help...if the unit is installed properly....

stephenmatlock

Thanks, everyone. Sorry, being Christmas, I got busy. I'll get a picture and let you know. I suspect it is likely the drain line, first, or the water flow, second. I'll also see if the filter is plugged.

I have the guy coming out in two weeks to review the installation.

Jack

Also, Stephen, get into the manual and learn how to operate the controller. It will tell you a LOT of things about the water heater. It stores error codes, will read flow in tenths of a gpm and many other things. I know you don't want a hobby, or another hobby, but under the circumstances, and informed consumer is best.

stephenmatlock

Jack said:

I know you don't want a hobby, or another hobby...

I laughed at that.

I'll get the manual.

I've already taken the cover off to examine it, so it shouldn't be hard to use the manual to get more understanding.

AdamAlvin09

I'm also having kind of similar problem and it is frustrating. Did you find any fix? Please share so that I can fix it.

Erin Holohan Haskell

@AdamAlvin09, welcome to Heating Help. To make sure your question doesn't get buried at the bottom of an old thread, please start a new post. Thanks!

r67183

I have a Bosch Aquastar 240fx no condensing tankless water heater. Lately I notice that when calling for hot water the unit fires up, runs for about 30 seconds and then the flame stop, the exhaust fan slows down and about 15 seconds later the gas comes back on with flame to continue heating for about another 10-15 seconds and then the flame shuts off again. I have flushed the system, taken off the exhaust pipe to check for obstructions (none) and the heat exhanger looked good and clean (just some greenish oxidation on the copper heating fins) so I ruled out exhaust blockage. This unit is about 20 years old, no flashing codes to guide me to a diagnoses. Any suggestions? I called Bosch for some assistance and they simply told me they no longer carry parts which didn't answer my question of why the occasion shut down during operation.

Jamie Hall

Step one is to find out what is shutting it off. Failure to sense flame? No water flow? Problem with other safeties? Low gas pressure?