Rheem Tankless Flushing & Error Codes in Utah

Rheem tells owners to flush the heat exchanger regularly and to add a water treatment device or softener when the water is outside its specified levels. Its warranty’s water-quality chart allows total hardness up to 200 ppm. When scale does build up, Rheem’s control board can catch it and show code 1L. Utah water often comes close to Rheem’s limit or passes it, so 1L is a code many Rheem owners here will see sooner or later.

Reading the 1L code correctly

People search for “Rheem LC” and “Rheem IL” because they’re used to other brands. Rheem’s tankless troubleshooting manual (for the RTGH High and Super High Efficiency series) uses 1L: the digit one, then a capital L.

1L: lime build-up in the heat exchanger

The manual says 1L means lime build-up has been detected in the heat exchanger. It also says the unit must be drained and flushed. This is different from a calendar reminder. The control board has seen a sign of scale, so the build-up is already there.

Here’s why it happens. The heat exchanger is the coil of narrow tubing that the burner heats. Hard water carries dissolved calcium and magnesium. When that water heats up, the minerals come out of solution and stick to the inside of the coil as lime scale. The layer slows heat transfer and narrows the tubes, and the board notices. Harder water and higher temperature settings both speed this up.

If you see 1L, schedule a flush. Don’t keep resetting the heater and hoping it clears.

Code 88: the flush reminder

Code 88 is gentler. Rheem’s RTGH use and care manual lists it as a reminder to flush the heat exchanger and/or replace the water treatment filter. It asks for routine care rather than reporting a problem the board has found.

The same manual describes a maintenance notice that is off by default. Once switched on, it can remind you to flush after 500, 750 or 1,000 hours of operation. If you’ve never seen a flush reminder on your Rheem, the notice is probably off. Ask the technician to turn it on after the next flush.

P1: not enough water flow

P1 means there is not enough water flow to operate the unit. A tankless heater only fires when enough water moves through it. Scale can help cause P1 because it narrows the passages and clogs the inlet screen. So can a partly closed isolation valve, a clogged faucet aerator, or a low-flow fixture used alone. Check the simple things first, then call if it continues.

Rheem codes at a glance

The error code hub compares Rheem’s lime code with Rinnai’s LC and Navien’s E760.

Seeing a code? Call to book a descale

Rheem’s warranty and hardness rules

Rheem’s residential tankless limited warranty (for RGT and RGTH models) is direct. It says damage caused by lime, mineral build-up, or scale is excluded. A separate clause excludes damage from installations where water quality falls outside Rheem’s chart. That chart lists total hardness up to 200 ppm. Units of mg/L and ppm mean the same thing for drinking water.

So a Rheem on water above the chart, with no treatment, has a weak warranty on its most expensive part. A Rheem with a flush record and a softener has a much stronger case. Our warranty and scale guide goes into the records to keep.

How Utah water compares with Rheem’s chart

A few local figures, all in mg/L so they line up with Rheem’s number:

• Draper: WaterPro, which serves part of Draper, lists an average of 184.1 mg/L in its latest report. That’s WaterPro’s figure for its own customers, not a whole-city number, but it sits close to Rheem’s limit.
• South Jordan and West Jordan: both buy most or all of their water from the Jordan Valley Water Conservancy District. The district’s samples ranged from 16.0–381 mg/L, so some homes get water well over the chart.
• Orem: treated surface water from the Central Utah Water Conservancy District’s Don A. Christiansen plant, one part of Orem’s supply, measured 112–154 mg/L in Orem’s report. Orem’s own springs and wells push the city’s overall range higher.
• Spanish Fork: the city listed 231–349 mg/L.

For scale, the USGS calls water 121–180 mg/L “hard” and anything more than 180 mg/L “very hard”. Most of the figures above land in one of those two bands. More detail is in our Utah hard water guide.

Seeing a code? Call to book a descale

Rheem’s flush procedure, in outline

Rheem’s troubleshooting manual lays out the flush. Here’s the outline so you know what a full job involves. It doesn’t replace the manual, and any gas, venting or electrical work belongs to a technician.

Equipment. The manual calls for a submersible utility pump (Tankless Flush Kit RTG20124). That’s the Rheem/Ruud Tankless Flush Kit, which includes the pump. Hoses attach to the service ports on the isolation valves. If your heater has no isolation valves, read our isolation valve guide first.

Solution. The bucket holds 2 gallons of food-grade white vinegar. Vinegar is a mild acid that dissolves lime scale.

Circulation. The pump loops the vinegar through the heat exchanger for 45 to 60 minutes. The manual ties the time to how much scale there is and how hard the water is. With hard Utah water, the technician may need the longer end.

Rinse. Cold water then runs through for about 5 minutes to clear the vinegar out.

Ask the technician to clean the inlet screen as well and to confirm that 1L has cleared before leaving.

Slowing scale on a Rheem

Rheem’s own advice is to install a water treatment device or softener when your water is outside its levels. Code 88 even mentions replacing a water treatment filter, so Rheem expects some owners to have one. Treatment slows scale but doesn’t stop flushing. Compare softeners and cartridges on our scale prevention page.

Seeing 1L? Call to book a descale. For 88 or P1, a local tankless technician can flush the heater or handle a repair visit. Angi lists an average of $200 to flush a tankless heater; the technician sets the actual price.