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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.
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 scale from the minerals in your water. Water hardness varies across the South Shore, and harder water gets a unit here sooner. The fix is a heat-exchanger flush, and the prevention is regular descaling (and, on harder water, a softener). Catching it at LC instead of Code 14 is the easy, inexpensive path — it's the unit doing you a favor.
What causes LC
1. Hard-water scale
Minerals in the water deposit inside the heat exchanger over time. Water hardness varies across the South Shore — Quincy, Milton and Boston are on soft MWRA supply, while towns on their own wells and local sources run harder — and every tankless unit needs periodic descaling regardless.
2. Overdue descaling
Tankless heaters should be flushed roughly once a year, and more often on harder water. LC means it is due — or overdue.
3. No water treatment
On harder water, scale builds faster without a softener or filter. 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.
What you can safely check first
- Nothing is broken, so there is nothing to reset. The code clears once the heat exchanger has been descaled.
- Note how long it has been since the last flush. On South Shore water, once a year is the honest interval.
- Do not ignore it. The same scale left alone becomes an overheat fault (Code 14) and shortens the life of the unit.
When to stop and call us
LC is the unit booking its own maintenance. We descale the heat exchanger, clean the inlet filter, and check the other wear items while the unit is open.
Rinnai asking for a descale?
Book the flush. We descale the heat exchanger, clean the inlet filter, check the other wear items, and clear the maintenance counter.
Rinnai LC FAQs
What does the Rinnai LC code mean?
LC (often LC0) is a scale-buildup maintenance reminder. The unit detected scale accumulating in the heat exchanger and is telling you it needs a descale/flush — before the scale causes a real fault or shortens the unit's life.
Is the LC code an emergency?
No — it is a maintenance warning, not a breakdown, and the unit usually keeps working. But do not ignore it: the same scale, left alone, can lead to an overheat fault (Code 14) or reduced efficiency and lifespan.
Can I clear the LC code myself?
The code clears after the heat exchanger is properly descaled. Some handy owners flush their own unit with the right kit; many prefer we do it as part of annual service so it is done correctly and other wear items get checked at the same time.
How much does a Rinnai descale cost?
The $99 service fee sends a licensed technician out to diagnose the problem. Approve the repair on the spot and the fee is not charged at all; decline it and the $99 covers the visit. A descale/flush is straightforward maintenance — far cheaper than the repairs that scale eventually causes if the LC warning is ignored.
Other codes on this unit? See all Rinnai error codes.
Why South Shore homeowners choose Johnson Bros.
Book the Rinnai descale
LC is maintenance, not a breakdown. Booking it now is what stops it becoming a Code 14 overheat later.
Not sure what's wrong? Send a photo or videoBooking online is the quickest way to hold the next open appointment. Call instead if it is urgent and you would rather talk to someone.
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Book the Rinnai descale
LC is maintenance, not a breakdown. Booking it now is what stops it becoming a Code 14 overheat later.
Call for urgent help now. Book online when you want the next available fit for your schedule.