Rinnai RUC98 Stops Heating after in use for awhile, No Error Codes

Tadpole548

I have a Rinnai RUC98 water heater installed in my garage. It was installed new with a new build house in 2016. For the last month or so it has intermittently stopped heating the water (typically noticed while showering). We would turn the water off for several seconds then back on and it would start heating again. I have checked several times during the issue and no error codes were listed on the front of the water heater. It was lasted de-scaled middle of April. A couple weeks ago, I checked the vent and did have to remove (2) small wasp nests. (1) was located in the center vent pipe, the other was located in the outer air intake pipe. It seemed that we did not have the issue again for about a week and then it has happened a couple more times. Nothing is located in the vent.
Also, noticed that my venting may be incorrectly installed. There is a concentric vent installed, however, the exhaust adapter was not removed and the intake cap is not installed. Pictures attached below.

Larry Weingarten

Hi @Tadpole548 , You may want to read through this: https://www.manualslib.com/products/rinnai-ruc98i-3726887.html ...and double check the venting. If it still doesn't work correctly after that, I'd contact customer service at Rinnai.

Yours, Larry

Tadpole548

Thanks Larry. I appreciate your reply! I will let you know what I find out.

Tadpole548

To all that may come across this thread, I had a plumber look at the issue and it was determined that the newish shower head installed in the master bathroom had a water saver included in it. It was not drawing enough flow to activate the water heater. He pulled out the water saver and I have not had an issue since (just shy of a year). Hope this helps.