If your Rinnai tankless water heater is flashing an error code, running cold, or short-cycling, most issues trace back to a handful of causes — venting, ignition, gas supply, or (very common in San Diego) hard-water scale. Drain Masters is a family-owned, licensed San Diego plumbing company (CSLB #961878) with 22+ years of experience servicing tankless units across San Diego County, 24/7. Here is what the most common Rinnai problems mean and when to call a pro.
Common Rinnai tankless problems we see in San Diego
- No hot water / unit won’t fire — often gas supply, ignition, or a tripped safety.
- Lukewarm or fluctuating temperature (“cold-water sandwich”) — flow, mixing, or scale on the heat exchanger.
- Error code on the controller — the unit is protecting itself; the code points to the system (see below).
- Reduced flow / longer wait for hot water — scale buildup from San Diego’s hard water is a leading cause.
- Rumbling, clicking, or exhaust smell — venting or combustion issues that need a licensed tech, not DIY.
Rinnai error codes: the three you’ll see most
Your Rinnai displays a numeric code when it shuts down for safety. Three of the most common:
| Code | Commonly indicates | What to do |
|---|---|---|
| 10 | Air-supply or exhaust (venting) blockage | Check vent terminal for obstruction; if clear, call a pro. |
| 11 | No ignition (gas/igniter) | Confirm gas is on and other gas appliances work; then service. |
| 12 | Flame failure during operation | Often gas-pressure or combustion; needs a licensed tech. |
For the full list of Rinnai codes and their meanings, see our detailed guide: Rinnai Tankless Water Heater Error Codes: Meanings and Fixes. If a code returns after a reset, stop and call a professional — repeated safety lockouts usually mean an underlying fault.
Why San Diego’s hard water is hard on tankless heaters
Much of San Diego County has very hard water (often 15–20+ grains per gallon). Every time your Rinnai heats water, minerals leave scale inside the heat exchanger — which chokes flow, hurts efficiency, and triggers maintenance codes over time. Rinnai recommends periodic descaling; in hard-water areas like ours, annual descaling (and a whole-home water softener) can add years to the unit’s life. Ask us about tankless service and descaling.
Repair or replace your Rinnai?
A well-maintained Rinnai can run 15–20 years, so most in-service units are worth repairing — especially for venting, igniter, flame-rod, or flow-sensor issues. Consider replacement when the unit is near end of life, the heat exchanger is failing, or repeated repairs are adding up. We give an honest recommendation, not a sales pitch — and a written estimate before any work.
How much does Rinnai repair cost?
Cost depends on the fault — a descaling/maintenance visit is modest, while a heat-exchanger or gas-valve repair costs more. Rather than guess, we diagnose the unit first and give you a clear, written price up front. Emergency and same-day service is available across San Diego County.
Why San Diego homeowners call Drain Masters
- Family-owned, licensed & insured — CSLB #961878, 22+ years in San Diego County.
- 24/7 emergency service; same-day appointments available.
- Straight answers and written estimates before work begins.
- Full plumbing shop: water heaters, drain cleaning, leak detection, and more.
Frequently asked questions
How do I reset my Rinnai tankless water heater?
Turn the unit off at the controller (or the remote’s on/off), wait a moment, then turn it back on to clear the code. If the same code returns, it’s signaling a real fault — call a licensed plumber rather than repeatedly resetting.
Why is my Rinnai running out of hot water?
Common causes are undersized capacity for simultaneous demand, low gas pressure, a dirty inlet filter, or scale on the heat exchanger from hard water. A technician can pinpoint which one and restore full output.
How often should a tankless water heater be descaled in San Diego?
Because of our hard water, once a year is a good rule — more often for large households or very hard water. Regular descaling protects efficiency and prevents scale-related error codes.
Is a flashing error code an emergency?
Not always, but a code means the unit shut down to protect itself. If you smell gas, leave and call your gas utility first. Otherwise, one reset is fine — if the code returns, book a service call.
Do you service all Rinnai models?
Yes. We service and repair Rinnai tankless units throughout San Diego County, and we install and replace them when repair no longer makes sense.
Rinnai acting up? Don’t sit in a cold shower. Call Drain Masters at (619) 346-4212 for fast, licensed tankless water heater repair anywhere in San Diego County — 24/7.