Rinnai RUR160i intermittent "dropping the ball" during showers, with bizarre codes

Smithery

We have a Rinnai RUR160i, installed new in September 2021.

Over the last few weeks, we've had this pattern repeat in most showers:

- Shower starts hot as it should
- Stays hot for 5+ minutes
- Goes cold over the course of ~15s
- Stays cold for ~30s
- Heats back up to full heat

If the shower lasts long enough, the cycle could repeat again.

We don't think this is unique to showers, per say. We just don't think we leave any other hot water on long enough to trigger the cycle. It does occur for showers in both bathrooms.

Following the procedure in the manual to retrieve stored diagnostic codes, there were none.

Tonight I finally found the time to leave the shower on while recording the display to see if anything happened in real time when the cold water cycle occurred.

Indeed, I could see that the "In Use" light was on while the shower was on (of course)... Then it turned off for about a second and then back on.

But then here's the crazy thing: A little while after the "In Use" light cycled, the temperature display flashed a series of codes. I have them on video, and they are, in this order:

01 02 03 04 05 06 07 08 09 10 11 12 15 19 20 21 A0 A1 A2 C0 C1 C2

After cycling through those codes, the temperature display goes back to 120 (the set point)

I've now witnessed the pattern 2.5 times (only caught it halfway through one of the times), same codes.

We *do* plan to get the installer out here, especially since it's well within the first year of warranty, but getting their schedule to match with ours is not something that will happen for a few more weeks... And I'm hoping to find some wisdom before that time.

This ring a bell for anyone?

neilc

what temperature do you have it set to?

Larry Weingarten

Hi, Do you know about how much hot water is flowing? Or, what is the gpm of the shower head? Also, is your water hard? A thought is to run hot water at a bath sink when showering to see if this keeps the heater on.

Yours, Larry

Smithery

neilc said:

what temperature do you have it set to?

120º

Smithery

Larry Weingarten said:

Hi, Do you know about how much hot water is flowing? Or, what is the gpm of the shower head? Also, is your water hard? A thought is to run hot water at a bath sink when showering to see if this keeps the heater on.

We have two shower heads in our master bath shower. The app says the flow rate is either 16 or 17, but who the hell knows what units those are? Certainly not gallons 😅

The wife thinks this behavior reproduces even with a wide-open tub fill, but haven't verified since I started exploring in depth. Will do tomorrow sometime.

Hypothetically if running an additional hot water tap fixes it, what would the diagnosis be? (The shower heads *really are quite enough* to trigger the damned thing...)

Larry Weingarten

Hi, "Hypothetically if running an additional hot water tap fixes it, what would the diagnosis be? (The shower heads *really are quite enough* to trigger the damned thing...)" It could be a problem with the flow switch, which could be caused/affected by hard water. Still, it sounds like you have good flow, with two heads running. Have you tried Rinnai tech support? You've gathered up some good data to show them.

Yours, Larry

neilc

Smithery said:

neilc said:

what temperature do you have it set to?

120º

I run my hot water at 110 tops, so I don't mix much, if any, cold in at the shower, which is low flow,

psb75

The 16 or 17 may be litres/min. If so, that is about 1/2 of the capacity of that unit. Specs say that it can supply 9 gpm. !!