Drain, flush and descale: what is the difference
These words get mixed up. Here is how they differ.
| Term | What it means | When you do it |
|---|---|---|
| Drain | Remove the water from the unit | Before servicing, moving the unit or protecting it from cold |
| Flush | Run water or solution through the heat exchanger | Routine maintenance on the maker's schedule |
| Descale | Dissolve mineral buildup with an approved solution | When scale shows up or the manual calls for it |
| Clean the filter screen | Remove debris from the inlet filter | At every service and when flow drops |
Many people do all four in one visit. The order below reflects that.
Before you start
Gather these first so the job does not stall halfway through.
- Find the manual or the model number so you can follow the exact procedure for your unit.
- Confirm the unit has service valves with ports, because without them a flush is much harder.
- Get a small circulation pump and hoses if your model calls for them, along with a bucket.
- Buy only the cleaning solution the manufacturer approves, since some products can harm seals or parts.
- Clear the work area and keep towels handy, because a little water will spill.
- Know where the gas shutoff and the electrical disconnect are for the unit.
The steps at a high level
Treat this as an outline and follow your manual wherever it differs.
- Shut off power or fuelTurn off the electric supply or close the gas control, then let the unit cool down. Never work on a hot or powered unit.
- Close the isolation valvesShut the cold and hot service valves so water in the house stays put while you work.
- Connect hoses and circulateAttach hoses to the service ports and run the approved solution through the unit with the pump for the time the manual states. Use vinegar only if the maker allows it.
- Drain and rinseEmpty the solution, then flush with clean water until the discharge is clear.
- Clean the filter screenRemove the inlet screen, rinse away debris and put it back carefully.
- Reopen valves and restartOpen the valves, bleed air from a hot tap and restore power or fuel. Then check for leaks and test the temperature.
How often should you do it?
Follow the interval in the manufacturer instructions for your model. Makers set the schedule based on how much scale their design can tolerate, and some service terms depend on following it.
Water hardness shifts the answer. A home with hard water may need more frequent attention than one with soft water. If you do not know your supply's hardness, the water utility publishes a yearly report, and your manual will say how to adjust.
Protecting the unit in a cold snap
Draining is also used to protect a unit that sits in an unheated space. If the heater is in a garage, crawl space or outbuilding, water left inside can freeze and crack the heat exchanger when the weather turns. Many tankless units have built in freeze protection, but it only works while they have power.
If you will be away or the power may go out, check the manual for the winterizing steps for your model. Freeze depth and local conditions in Millville are not something we can state here, so plan for the coldest nights rather than the average ones.
Why Millville's soft water changes the picture
The City of Millville Water Utility's 2026 Consumer Confidence Report lists carbonate hardness of 29 ppm, which is soft water by common classification. That means mineral scale builds more slowly in a heat exchanger here than in hard water areas, so heavy scale is less likely to be your main problem.
Even so, do not skip the schedule. Sediment can still collect, the inlet screen can clog, and the maker's maintenance terms still apply. Soft water lowers the urgency of descaling, but it does not replace the routine.
Source type: City of Millville Water Utility web page and 2026 Consumer Confidence Report.
Signs the unit needs attention now
Watch for reduced flow, water that takes longer to heat, rumbling or popping from the heat exchanger, or error codes that mention flow or temperature. A unit that shuts off mid shower may have a clogged screen or a deeper fault.
If a flush does not help, the problem may be a failed sensor or igniter, and that is a repair job. Our tankless water heater page explains how repair and flushing fit together, and water heater repair covers the tank side.
When to hire it out
Hire a plumber if the unit has no service valves, if you cannot find the manual, if you smell gas, or if the unit leaks after you finish. Call for help also if you are not comfortable working near gas or electricity.
If you ever smell gas, leave the building, then call 911 and your gas utility from outside. Do not turn on lights or try to find the leak yourself.
For help in nearby areas, our Bridgeton plumber and Vineland plumber pages show where we serve beyond Millville.
Questions People Ask
Only if the manufacturer says so. Some makers allow food grade vinegar and others require a specific solution. Using the wrong product can damage parts.
A softener reduces scale, but the unit still collects sediment and the filter screen can clog. Follow the maker's schedule for your model.
A flush is much harder without them. A plumber can add isolation valves, which also makes later service easier.
It varies by model and by how much buildup there is. Your manual gives the circulation time for the cleaning solution.
Not by hardness alone. The city reports soft water. Sediment and a clogged inlet screen can still hurt performance, so keep up the maintenance.
Check the manual for the winterizing steps first. If the heater is in an unheated space and power or heat may be lost, draining it and the lines is a common precaution. Ask a plumber if you are unsure which valves to close.
Sources and standards
These are the references behind the guidance on this page. Rules and contacts change, so confirm details with the agency.
- New Jersey Uniform Construction Code, plumbing subcode (the Millville Construction Office posts the permit form)
- State Board of Examiners of Master Plumbers, Division of Consumer Affairs, for checking any plumber's license
- Manufacturer installation and service instructions for your specific unit