Tankless Water Heater Maintenance in Ottawa: How to Flush and Descale Your Unit
A tankless water heater heats water only when you open a tap, so every litre passes through a compact heat exchanger. In Ottawa homes with hard water, mineral scale can coat that heat exchanger over time and cut hot water performance. A periodic flush, also called descaling, is the standard fix, and it is the single most useful maintenance job for a tankless unit.
Prefer to have a plumber handle it? Book water heater maintenance in Ottawa or call 613-227-7465.
At a glance
- What it is: a flush circulates a descaling solution (commonly white vinegar) through the heat exchanger to dissolve mineral scale.
- How often: many manufacturers recommend at least once a year, and more often in hard water. Your unit manual has the final word.
- Time: the solution is commonly circulated for about 45 minutes to an hour, plus setup and rinse.
- Biggest risk: skipping the flush until the unit shows error codes or runs lukewarm.
Why Tankless Water Heaters Need Maintenance in Ottawa
Hard water carries dissolved calcium and magnesium. When water is heated, those minerals can separate out and harden as scale on the hottest surfaces. In a tank-style heater, much of it settles at the bottom. In a tankless unit the hottest surface is the narrow heat exchanger, so even a thin layer can restrict flow and make the unit work harder.
Water hardness is not the same across the Ottawa area. Homes on city water and homes on private wells in rural parts of the region can see very different mineral levels, so the right flush schedule depends on your water. If you are unsure, our guides on how to tell if you have hard water and water softener installation are good places to start.
Signs Your Tankless Water Heater Has Scale Buildup
Scale does not announce itself. These are the symptoms plumbers most often connect to it:
| What you notice | What it can mean |
|---|---|
| Hot water is lukewarm or takes longer to arrive | Scale is restricting flow through the heat exchanger |
| Temperature swings in the shower | The unit is struggling to hold its set temperature |
| Rumbling, popping or kettle-like noises | Water is trapped under scale and boiling in small pockets |
| Error codes or the unit shuts itself off | Overheating or flow sensors reacting to restricted flow |
| White flakes in faucet aerators | Hard water minerals are present in your supply |
Note: These symptoms can also point to a gas supply, venting or sensor problem, so scale is a likely cause but not a certain one. If a flush does not restore performance, the unit needs a proper diagnosis. Our tankless water heater service in Ottawa covers repairs as well as installs.
How Often Should You Flush a Tankless Water Heater?
Short answer: at least once a year is the common manufacturer guidance, and homes with hard water may need it more often. Check the maintenance section of your manual, because intervals and approved descaling solutions differ between brands. Following the manual also helps keep your warranty position clear.
| Your situation | Reasonable approach |
|---|---|
| Softened water, newer unit | Annual check and flush per the manual |
| Untreated hard water | Flush on the manufacturer interval or sooner if you see the signs above |
| Private well water | Test the water first, then set the schedule around the results |
| Unit installed years ago and never flushed | Book a professional flush before trying anything yourself |
How a Descaling Flush Works, Step by Step
This is the general process. Models differ, so the manual for your exact unit takes priority.
Shut off power and fuel
Turn off the electrical supply, and for a gas unit close the gas valve. Let the unit cool.
Close the water valves
Shut the cold and hot isolation (service) valves. Units without isolation valves need them added before a proper flush is possible.
Connect the flush kit
Attach hoses to the service ports, with a small submersible pump and a bucket of descaling solution (commonly white vinegar) in a loop.
Circulate the solution
Run the pump so the solution cycles through the heat exchanger, commonly for about 45 minutes to an hour.
Rinse thoroughly
Drain the solution, then flush the unit with clean water so no vinegar remains in the lines.
Clean the inlet filter and restart
Remove and rinse the cold-water inlet screen, reopen the valves, check for leaks, restore power and fuel, and test hot water.
Safety first: Never work on a gas tankless unit if you smell gas. Leave the home and call your gas utility. Combustion, venting and gas connections are work for a licensed professional.
Should You DIY a Tankless Flush or Call a Plumber in Ottawa?
| DIY flush | Professional flush | |
|---|---|---|
| Tools | Pump, hoses, bucket, vinegar | Equipment and fittings on the truck |
| Isolation valves | Must already be installed | Can be checked, and added if missing |
| Diagnosis | Limited to what you can see | Checks venting, filters, flow and error codes |
| Best for | Comfortable owners with a newer, easy-access unit | Older units, gas units, hard water, or any unit that has never been flushed |
A flush is a reasonable job for a confident homeowner, but a unit that has gone years without one can have heavy scale and may reveal other issues once opened up. If you would rather not risk it, contact John The Plumber and we will look at your unit.
Tankless water heater not heating like it used to?
Call John The Plumber in Ottawa for maintenance, flushing or repair.
Tankless Water Heater Maintenance FAQs for Ottawa Homeowners
How do I know if my tankless water heater needs descaling?
Can I use white vinegar to descale a tankless water heater?
How long does flushing a tankless water heater take?
Does a water softener replace tankless maintenance?
Will flushing fix a tankless heater that has stopped working?
Do I need isolation valves to flush a tankless water heater in Ottawa?
Who can service my tankless water heater in Ottawa?
Book Tankless Water Heater Maintenance in Ottawa
Call 613-227-7465 or visit johntheplumber.ca to schedule a flush or an inspection of your tankless unit.
Related reading: Stop renting water heaters and Home Protection Plans.
