What scale does inside a tankless unit
Where a tank collects loose sediment at the bottom, a tankless heater collects scale on the walls of its heat exchanger. The passages are small, so even a thin layer makes a difference: heat transfers less efficiently, flow drops, and the exchanger can overheat in spots.
Many tankless units watch for exactly these conditions and display a code when they see them. A code is not always a part failure; often it is the heater telling you it needs maintenance.
Signs a tankless unit needs attention
- Hot water that fluctuates or goes cold mid-shower
- Lower flow at hot taps than cold ones
- A maintenance or scale reminder on the display
- The unit shutting down and showing an error code
- Longer waits before hot water arrives than when new
What error codes commonly relate to
| Code category | Common causes | First step |
|---|---|---|
| Ignition or flame failure | Gas supply, ignition parts, venting | Check other gas appliances; call a plumber if gas is fine |
| Overheating or exchanger temperature | Scale buildup, low flow | Look up the code; descaling may be due |
| Low flow or flow sensor | Clogged inlet filter, scale, fixture aerators | Check whether the manual describes cleaning the inlet filter |
| Venting or exhaust | Blocked or damaged vent | Turn the unit off and have the venting checked |
| Maintenance reminder | Scheduled descaling interval | Arrange a descale |
How descaling is usually done
Most manufacturers describe a flushing procedure using isolation valves on the water lines. Follow your manual; if your unit has no service valves, a plumber can add them.
- Power and gas off.Turn the unit off at its controls and power, and close the gas valve to the unit.
- Isolate the water.Close the service valves so the unit is separated from the house plumbing.
- Circulate descaling solution.A small pump circulates a manufacturer-approved solution through the exchanger for the recommended time.
- Flush and restore.Flush with clean water, clean the inlet filter, reopen the valves, and restore gas and power.
Questions for a tankless service visit
- What did the code mean on this specific model?
- How heavy was the scale, and how often should it be descaled here?
- Are service valves installed, and are they working?
- Is the gas supply and venting adequate for this unit?
Common questions
- Can I clear a tankless error by resetting it?
- Some codes clear after a reset, but if the underlying cause remains, it comes back. Note the code and look it up before resetting repeatedly.
- Does a water softener help a tankless heater?
- Reducing hardness reduces scale. Whether a softener or another treatment suits your home is a separate decision worth discussing with a plumber.
- Is descaling a do-it-yourself job?
- Some homeowners do it following the manual. It involves gas and power shutoffs and chemicals, so many prefer a plumber.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.