Direct answer: For a Rheem Preferred RHS32 or Preferred Plus RHS42, set the clock, measured hardness and a low-use recharge time with the SELECT and arrow buttons. Both reviewed 2026 controllers have NaCl/KCl salt-type selection, but their salt-level controls differ: RHS32 uses a SELECT menu; RHS42 has a dedicated SET SALT LEVEL button. The factory hardness number is not a water-test result for your home.
Publisher boundary: Water System Guide is an independent research publisher, not Rheem water-treatment support or an authorized repair service. This guide covers RHS32 and RHS42 controls in the manufacturer manuals Rev. P dated January 20, 2026, reviewed October 7, 2026. RHS18, RHW42 WiFi functions and replacement controls need their own matched instructions.
Identify the model and keep the current values
Read the rating label inside the salt lid, then compare the actual button layout with the manual. Rheem’s model-code instructions identify rH32 for RHS32 and rH42 for RHS42. RHW42 also uses rH42, so a code reading alone does not identify the complete model.
Photograph the display and record the current settings before making a change. That gives support a starting point if the system’s behavior changes. A different menu or replacement controller is a reason to confirm its manual rather than continue with a similar-looking model’s sequence.
| On the reviewed control | RHS32 | RHS42 |
|---|---|---|
| Time screen | SET TIME | PRESENT TIME |
| Hardness and recharge time | SELECT menu and arrows | SELECT menu and arrows |
| NaCl/KCl salt type | SELECT menu and arrows | SELECT menu and arrows |
| Salt-level monitor update | SELECT to SET SALT LEVEL, then arrows | Dedicated SET SALT LEVEL button |
| Extra Clean Feature menu | Not listed in the reviewed optional-menu sequence | Listed as a separate optional feature |
Sources: RHS32 manual, pages 13–17, RHS42 manual, pages 13–18, and model-specific salt-level support. This table is for matching the controls, not identifying them solely by a product photo.
Set the present time and check AM/PM
Press SELECT until the time-setting screen appears. Use the arrows to set the present time and check the AM/PM indicator. Press SELECT to continue. Rheem’s programming guide explains this normal setup sequence.
After a power interruption, a flashing clock may need correction. Do not assume that the hardness value and every other setting were erased. First record what the controller shows. A correct clock matters because recharge should happen during the intended low-use period.
Calculate hardness from actual water results
The hardness menu uses grains per gallon (gpg). Rheem’s hardness-programming instructions give these two distinct calculations:
- A hardness result reported as mg/L or ppm as calcium carbonate is divided by 17.1 to convert to gpg.
- For measured ferrous/clear-water iron, add 5 to the programmed hardness number for each 1 ppm of that iron.
For example, 15 gpg hardness + (2 ppm clear-water iron × 5) = a programming number of 25. This is an illustrative controller compensation, not a statement that the water contains 25 gpg of measured hardness or that its iron concentration became 10 ppm. Keep the actual test results and the programmed number in separate fields.
The reviewed manuals show a factory hardness value of 25. A home can have a different value; do not select 25 merely because it appears after setup. Our water hardness calculator helps organize unit conversion.
Confirm that iron is the type and amount the unit can handle. Manual page 6 distinguishes clear-water iron from red-water, bacterial and colloidal forms. An iron-compensation formula does not establish that a softener can treat those other forms. For uncertain well-water chemistry, get a water assessment before changing the setting.
On the normal HARDNESS screen, use the arrows to enter the supported number, then SELECT to continue. Increasing the number at random is not a reliable way to make water softer; confirm treated-water hardness and demand if performance remains poor.
Choose a recharge start time, not a fixed weekly schedule
The reviewed default start time is 2:00 a.m. Choose a period when your household normally needs less water and check AM/PM. Rheem’s programming guide describes typical recharge duration as roughly two to two and a half hours; this is not an exact timer for every configured cycle.
The start-time setting tells the unit when a called-for recharge should begin. Metered demand determines how often it is needed. Water used during recharge can bypass treatment, so a household whose work schedule makes overnight water use common may need a different start time.
The optional maximum-days setting is a separate limit. Rheem’s maximum-days explanation says the unit can recharge sooner than that limit. Setting seven days, for example, does not guarantee one cycle every seven days. Have support or the installer explain why an override is appropriate before imposing extra cycles.
Select the salt type without applying the wrong KCl rule
Both reviewed Rev. P manuals include a NaCl/KCl selection in the normal programming sequence. Use the arrows on that screen to match the salt actually used, then SELECT to continue.
Rheem’s KCl-specific instructions distinguish controllers with a salt-type menu from those without one. For controllers with that menu, select KCl there. The article’s extra 25% hardness adjustment applies to controllers without the menu. Do not automatically add that adjustment as well on these two matched controls.
The broader hardness article uses less qualified wording. The model manuals and the salt-specific article provide the applicable detail here. If your installed control lacks the menu despite the model label, confirm the controller version with support before applying a workaround.
Update the salt monitor when you add salt
Look at the physical salt level beside the numbered brinewell scale. The displayed monitor needs to be updated to match it; changing the display does not add salt or repair a salt bridge.
For RHS32, tap SELECT until SET SALT LEVEL appears, use the arrows to match the observed level, then SELECT back to the clock. For RHS42 with the dedicated button, press SET SALT LEVEL until the display bars match the observed numbered level. These distinct procedures come from Rheem’s salt-level instructions.
If the low-salt warning persists after refilling, record both the actual level and the display. Do not disable the monitor merely to make a light disappear. If salt is present but not being used, follow the not-softening guide rather than changing only the estimated level.
Optional settings need a reason
The E indication identifies the enabled efficiency feature, not an error code. Rheem’s explanation says it can mean more frequent recharges using smaller salt and water quantities. Follow the matched manual’s location-specific efficiency instructions when commissioning the system.
The RHS42 also has an extra Clean Feature menu; this is different from the periodic CLn cleaner reminder. Avoid copying its settings into the RHS32. Backwash, rinse and diagnostic menus are not general cures for every hard-water complaint. Ask support to match any adjustment to the actual symptom and record the original value.
Keep a settings record beside the manual
Use one line for each item: equipment model and serial number; manual revision; raw hardness and units; clear-water iron result; programmed hardness; clock and AM/PM; recharge start time; salt type; physical and displayed salt level; optional settings; date and reason for the change; treated-water test afterward.
If the controller shows an error, the tank overfills or water remains hard after ordinary settings are confirmed, use the troubleshooting observations and arrange softener service. Internal wiring, valve repair and diagnostic cycle advancement need the matched service procedure and appropriate skill.
Frequently asked questions
What hardness should I set on a Rheem RHS32 or RHS42?
Use measured hardness in grains per gallon, with the supported compensation for measured clear-water iron when applicable. The reviewed factory value of 25 is not a recommendation for every home. Keep the test result separate from the programming number.
Do RHS32 and RHS42 use the same salt-level buttons?
No. The reviewed RHS32 control uses SELECT to reach SET SALT LEVEL and the arrows to set it. The reviewed RHS42 has a dedicated SET SALT LEVEL button that changes the displayed bars to match the physical salt level.
Should I add 25% to hardness when choosing KCl on these controls?
Rheem’s KCl-specific support article says to choose KCl in the salt-type menu when that menu is present. Its extra 25% hardness adjustment is for controllers without that menu. Both reviewed RHS32 and RHS42 manuals include the menu.
Does setting seven maximum days mean a recharge every seven days?
No. Maximum days is a limit, not a fixed interval. Metered demand can trigger recharge sooner. The recharge start time is a separate setting for the time of day.
Sources and review scope
- Rheem RHS32 manufacturer-authored and manufacturer-hosted owner manual 7386465, Rev. P January 20, 2026; reviewed October 7, 2026.
- Rheem RHS42 manufacturer-authored and manufacturer-hosted owner manual 7386473, Rev. P January 20, 2026; reviewed October 7, 2026.
- Rheem first-party Softener Programming Guide, updated August 3, 2026; reviewed October 7, 2026.
- Rheem first-party Hardness Level Programming, updated February 18, 2026; reviewed October 7, 2026.
- Rheem first-party Salt Level Programming, updated February 19, 2026; reviewed October 7, 2026.
- Rheem first-party KCl salt alternative instructions, updated February 19, 2026; reviewed October 7, 2026.
- Rheem first-party Programming the Model Code, updated February 19, 2026; reviewed October 7, 2026.
- Rheem first-party Maximum Days Between Recharges, updated February 19, 2026; reviewed October 7, 2026.
- Rheem first-party E Efficiency Setting, updated February 24, 2026; reviewed October 7, 2026.
The cited manuals and support pages were checked October 7, 2026. This review does not establish current retailer pricing, local inventory, performance in your home or the configuration of a different controller.