Where the scale comes from

Fullerton runs its own water utility, and its supply is local groundwater blended with imported water. That water carries dissolved calcium and magnesium. When water is heated, some of those minerals come out of solution and stick to hot surfaces. In a tank they settle as sediment at the bottom. In a tankless unit they coat the inside of narrow heat exchanger passages.

As the coating thickens, it insulates the metal, restricts flow and forces the burner to work harder. Eventually the unit may overheat, cycle, or display a scale or flow-related code. The white crust you see on faucets and shower heads around town is a good hint of what is building up inside the heater.

How a typical flush works

This is an outline, not a substitute for the manual. Steps differ by model, and if you are unsure, have a licensed plumber do it.

  1. Shut down safely.Turn off power to the unit and close the gas valve to it, following the manual's shutdown steps.
  2. Isolate the unit.Close the hot and cold service valves so the heater is separated from the house plumbing.
  3. Connect a pump and hoses.Hoses attach to the flush ports on the service valves, with a small pump circulating descaling solution from a bucket.
  4. Circulate the solution.The descaler runs through the heat exchanger for the time the manufacturer recommends.
  5. Rinse and clean the filter.Fresh water flushes out the solution, and the inlet water filter is removed and cleaned.
  6. Restore and check.Valves are reopened, air is purged, gas and power are restored, and the unit is tested for leaks and steady temperature.

Before you plan a DIY flush

  • The unit has service valves with flush ports on both the hot and cold lines
  • You have the manual and know the recommended descaling product
  • You can safely shut off gas and power to the unit
  • There is a place to safely dispose of the used solution
  • You are comfortable reopening gas and checking for leaks afterward

A sensible upkeep rhythm

Intervals come from the manufacturer; harder water may call for shorter ones. Ask your plumber what makes sense for your unit.

Each month
Glance at the display for codes and listen for unusual noise at ignition.
Every few months
Check the inlet filter if the manual calls for it, and look for drips at valves.
At the manufacturer's interval
Flush and descale the heat exchanger.
After any plumbing work
Clean the inlet filter; repairs can loosen debris, especially from galvanized pipe.

Questions for the plumber

  1. How often should this model be flushed with our water?
  2. Would a scale-reduction filter or water treatment help, and what upkeep does it need?
  3. Did you clean the inlet filter, and what did you find?
  4. Is there any sign of heat exchanger damage from past scale?

Common questions

Can I use plain vinegar to descale?

Some manufacturers allow it and others specify a particular descaler. Follow your manual so you do not risk the warranty or the heat exchanger.

What happens if I never flush?

Scale keeps building, reducing flow and efficiency. Over time it can cause overheating codes and shorten the heat exchanger's life.

Does a water softener remove the need to flush?

It can slow scale, but check the manufacturer's guidance and keep inspecting the unit. Ask a plumber whether treatment fits your home.

General information for Fullerton, not a quote or professional advice. In an emergency, call 911.