Rheem 88 Error Code: Maintenance reminder: flush heat exchanger or replace filter
Updated October 2026 · Sourced from Rheem documentation
The manual says this is a reminder to flush the heat exchanger and/or replace the water treatment filter. It appears after a set number of combustion hours when the optional maintenance notice is on.
Is it safe to keep running? Usually yes. The manual says to contact a dealer or qualified service technician for the flush or filter replacement, and to do that maintenance before the code is cleared.
88 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| 88 Shown on the LED display of the remote control | Maintenance reminder: flush heat exchanger or replace filter | Rheem non-condensing tankless gas water heaters (160,000, 180,000 and 199,900 Btu/h models) with remote control display |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Note that this is a maintenance reminder, not a breakdown code.
🛑 Stop and call a licensed pro if
- The manual says to contact a dealer or qualified service technician for the flush or filter replacement, and to do that maintenance before the code is cleared.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Codes for flame failure, overheating, venting or the control board that return after one reset.
- Water leaking from the heater, the relief valve discharging, or scorching around the burner area.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Rheem code
- Write down the exact code shown on the controller or the number of status light flashes.
- Turn the water heater power off and back on (or press the reset button the manual describes) once. If the code comes back, stop resetting.
- Make sure the gas supply valve to the heater is open and other gas appliances in the home are working.
- Make sure the cold water supply valve is fully open and hot water taps are not partly closed.
- Look at the outside vent terminal for snow, ice, leaves or anything blocking it (look only).
Source: Rheem High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual, Service Error Code Chart, p. 77 and p. 78-79. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
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