Tankless water heaters are efficient and long lived, but they have one weakness: mineral scale. As hard water passes through the narrow heat exchanger, calcium and magnesium build up, restricting flow and making the burner work harder. Eventually you get fluctuating temperatures and error codes.
Descaling once a year prevents most of that. Here is what the process involves, so you can decide whether to do it yourself or book it.
Signs your unit needs descaling
Scale builds up gradually, so the symptoms creep in.
- Water temperature swings during a shower.
- Lower hot water flow than when it was new.
- Scale or descale reminder error codes on the display.
- A unit that is louder than it used to be.
What you need
A proper flush requires service (isolation) valves on the hot and cold lines at the unit. Most professional installations include them. You also need a small submersible pump, two hoses, a bucket and a descaling solution suitable for your model. Check the manual, since some manufacturers specify what to use.
The basic process
Every model is slightly different, so follow your manual. The general steps are below.
- Turn off power and close the gas valve to the unit.
- Close the hot and cold isolation valves.
- Connect hoses from the pump to the cold service port and from the hot service port into the bucket.
- Open the service ports and circulate the descaling solution, usually for about an hour.
- Flush with clean water, clean the inlet filter, close the ports and reopen the valves.
- Restore gas and power and run a hot tap to clear air.
If your unit has no isolation valves, or you are not comfortable working near gas connections, book the flush. Adding service valves is a small job that makes every future flush easier.
Call (289) 801-7262Not sure it's a DIY fix?
Describe the symptom over the phone and a HeatNest technician will tell you what it likely is and what a repair involves.
Call (289) 801-7262While you are there
A professional maintenance visit adds checks you would not normally do yourself: burner and flame inspection, venting and condensate line checks, error history review and combustion testing. That combination is what keeps a tankless unit running well for many years.
Should you add a water softener?
In very hard water areas, a softener or scale prevention system can reduce how fast scale builds. It does not eliminate maintenance, but it can stretch the interval and protect other fixtures in the house.
Common questions
+How often should a tankless water heater be flushed?
Most homes should flush once a year. Very hard water may need it more often.
+Can I use vinegar to descale?
Some manufacturers allow it, others specify a particular solution. Check your manual first.
+What happens if I never descale?
Scale reduces performance, causes error codes and can eventually damage the heat exchanger.
+How long does a professional flush take?
Usually about an hour to an hour and a half, including inspection.
+Does descaling affect my warranty?
Many manufacturers expect regular maintenance. Check your warranty terms.