What scale does inside the heater
Fullerton's water utility delivers a blend of local groundwater and imported water, and it carries enough calcium and magnesium to be considered hard. Heating water drives those minerals out of solution, and in a tankless unit they deposit on the narrow passages of the heat exchanger where the water gets hottest.
A thin layer acts like insulation. The burner has to work harder to deliver the same temperature, the exchanger runs hotter than it should, and the unit's sensors start to notice. Left long enough, scale can restrict flow, cause temperature swings and trigger overheat or flow codes.
Signs a unit is due for descaling
How a typical flush is done
Methods vary by model. This is the general sequence a plumber follows using the service valves under the heater.
Shut down the unit
Turn off power and gas to the heater and close the hot and cold isolation valves.
Connect a pump loop
Hoses attach to the service ports, with a small pump and a bucket of descaling solution recommended for that heater.
Circulate
The solution runs through the heat exchanger for the time the manufacturer specifies, dissolving deposits.
Rinse
Fresh water flushes out the solution and loosened scale.
Clean the inlet filter
The small screen on the cold inlet is removed, rinsed and reinstalled.
Restart and test
Valves open, air is purged, power and gas are restored and the unit is run at several faucets to confirm steady temperature.
Flushing alone or adding water treatment
Flush on schedule
- No new equipment to install
- Removes scale after it forms
- Needs to be repeated on the manufacturer's schedule
- Good fit when the rest of the house has little scale trouble
Add a softener or scale-reduction system
- Reduces how fast scale forms in the first place
- Adds equipment, space needs and its own maintenance
- Helps fixtures and appliances as well as the heater
- Ask whether the heater maker approves the treatment type
Questions before a descale
- What descaling solution will you use, and is it approved for my heater?
- Does my unit have service valves, and are they in good condition?
- How much scale did you find, and how often should I flush based on that?
- Is the inlet filter clean and the condensate drain clear?
- Would water treatment make sense for this house?
Common questions
Can I flush my own tankless heater?
Some owner's manuals describe an owner flush. If yours does and you are comfortable shutting off gas and power, follow it exactly. If gas, venting or valves are unclear, leave it to a licensed plumber.
My heater has no service valves. Is that a problem?
Without service valves a flush is harder. A plumber can tell you whether adding an isolation valve kit makes sense.
How often should I descale?
Follow your manufacturer's schedule. In hard water, many homeowners find they need to stay on the shorter end of whatever range the manual gives.
General information for Amerige Heights, not a quote or professional advice. In an emergency, call 911.