u/praeda-bot

Hey all,

In diagnosing a low water pressure problem when more than a few sinks/showers are on in the house, we concluded it's the water softner (comparing with bypass and without bypass). Results surprised me to be honest - anyway.
Even though it's not an old unit (6 years - from AFWFIlters), with the help of their support, decided it's the media gone bad, so I ordered more.
In the process of disassembling the unit and removing the media - I think the media is fine and it may be this black gunk in the head. The black stuff is kind of slimy/oily - I wish it was black gold, but it's not.
We have a Culligan whole house filter before the water softner and run 5micron carbon filters (Amazon - PUREPLUS 5 Micron 10" x 4.5") . Almost seems like carbon - only black thing I can think of.

Thoughts? Assuming I can tear this down a bit and clean?

Appreciate your time and any help.

I have a Rinnai RL94i that seems to be taking noticeably longer for hot water to reach the faucets. I know tankless units naturally have some delay, but this unit definitely used to deliver hot water faster.

Here’s what I’ve done so far:

I was getting a Code 10, indicating an air intake or exhaust issue. I found and removed several dirt dauber nests from the intake piping. The unit is installed indoors and vents outside. That appears to have resolved the Code 10.
Afterward, I began intermittently getting a Code 11. I replaced the igniter and flame-sensing electrodes with OEM parts. I also removed the burner assembly and thoroughly blew it out with compressed air ( I suspect some of the dirt dauber dirt fell into the burner tray). The ignition issue now seems to be resolved. I also took out the fan and cleaned - it wasn't bad.
Since the hot-water delay was still noticeable, I replaced both the water-flow sensor and the water-bypass valve.

I didn’t realize the unit had an internal bypass valve, and I’m not entirely sure how Rinnai uses it. Could a bypass-valve problem or incorrect operation cause hot water to take longer to reach the fixtures? Could failing thermistors cause similar behavior?

I also noticed that the burner appears to have four gas zones. The center zone (2nd from the left) ignites first, and additional zones seem to activate as flow increases, such as when running a shower or tub. I can confirm that at least the first and second zones, looking from left to right, ignite. I can’t clearly see the zone opposite the inspection window, but it does appear they light - the burner on the outside definitely feels hotter (compared to when a low flow sink with only the 2nd zone lit). Could a gas solenoid be failing to open one of the burner zones? My assumption is that this would cause problems reaching the target temperature, but the water does eventually get fully hot.

A few other details:

The delay is happening throughout the house, so I don’t think it is a clogged aerator or fixture-specific restriction.
I have already descaled the heat exchanger.
The water manifold did not appear to have significant buildup (outside fins) when I inspected it.
Once the hot water arrives, the temperature seems normal and stable.

What else should I be checking?

Appreciate any advice.

Black Gunk in Fleck 5600?

Rinnai RL94i taking longer than before to deliver hot water — bypass valve or thermistor issue?

LMS M86 Block 116 Row 1