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Rinnai LC Code — Scale Buildup (Maintenance)
Good news: LC isn't a breakdown — it's your Rinnai asking for a descale. It caught scale in the heat exchanger early, before it turns into a real fault.
What LC Means
The LC code (often shown as LC0) is a maintenance reminder, not a breakdown. Your Rinnai monitors for scale, and LC means it has detected enough buildup in the heat exchanger that it wants a descale — before the scale restricts flow enough to cause an overheat (Code 14) or shorten the unit's life.
The cause is hard water, which the South Shore has plenty of. The fix is a heat-exchanger flush, and the prevention is regular descaling (and, ideally, a water softener). Catching it at LC instead of Code 14 is the easy, inexpensive path — it's the unit doing you a favor.
Common Causes of LC
1. Hard-water scale
Minerals in hard water deposit inside the heat exchanger over time. The South Shore has hard water, so most tankless units here need periodic descaling.
2. Overdue descaling
Tankless heaters should be flushed roughly once a year (more with very hard water). LC means it is due — or overdue.
3. No water treatment
Without a softener or filter on hard water, scale builds faster. We can advise on whether treatment makes sense for your home.
4. Ignoring it leads to Code 14
LC is the early warning. Left alone, the same scale eventually restricts flow enough to trip an overheat fault. Handling LC now is the cheaper path.
Rinnai LC FAQs
Why South Shore homeowners choose Johnson Bros.
Rinnai showing LC? Tell us the model and we'll triage.
Every Rinnai model reads codes a little differently. Have your model number handy and we'll tell you whether it's a quick fix or a service visit.
Need help fast? Call for urgent plumbing issues. Booking online is best when you want the next open appointment without waiting on the phone.
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Rinnai showing LC? Tell us the model and we'll triage.
Every Rinnai model reads codes a little differently. Have your model number handy and we'll tell you whether it's a quick fix or a service visit.
Call for urgent help now. Book online when you want the next available fit for your schedule.