Tankless Water Heater Maintenance in BC: When to Flush & What to Check

A tankless water heater has no tank to drain, so the usual advice about flushing a hot water tank doesn't really apply. The maintenance is different. Instead of draining sediment out of the bottom of a tank, you're dissolving mineral scale off the inside of a heat exchanger, cleaning a small filter, and checking the venting.

How often that needs to happen depends on two things: what your manufacturer says and what's in your water. If your home is on Metro Vancouver's water system, your water is very soft, and that changes the answer. If you have a conventional tank, our post on how often to flush your hot water tank in BC is the one you want. This one is for tankless owners.

What "flushing" a tankless unit means

Navien compares it to descaling a coffee maker. As water is heated, minerals build up on the waterways inside the heat exchanger. Navien says those deposits can erode and clog the heat exchanger, cut efficiency and flow, and lead to early failures.

The fix is to close the unit's hot and cold service valves, hook hoses and a small pump to the service ports, and circulate a descaling fluid through the heat exchanger from a bucket. Then it gets rinsed with fresh water. The details depend on the brand:

• Navien says to use an approved tankless descaling solution or white vinegar, circulate it for at least 45 minutes, and rinse with fresh water for at least 10 minutes.

• Rinnai's flushing procedure calls for 4 gallons of undiluted white vinegar, and says never to use chemical solutions, because the water that runs through the heater is the water you drink and bathe in.

• Noritz recommends pumping kitchen-grade vinegar through the system for about an hour.

Since the brands don't agree on what to circulate, go by the manual for your model.

How often should you flush it?

There isn't one schedule that covers every brand. Here's what three manufacturers publish:

• Navien's general advice is to descale at least once a year, and more often if your water has more minerals, your temperature is set higher, or your household uses a lot of hot water. Its installation manual for the NPE-A2 and NPE-S2 condensing models gets more specific with a hardness table. Soft water (0 to 60 mg/L) lists no flush. From 61 to 200 mg/L, it's once a year for homes if no water treatment is installed. Above 200 mg/L, a softener or Navien's PeakFlow system is required. The same manual says damage caused by poor water quality isn't covered under warranty.

• Rinnai says to flush mineral deposits at least once a year. Its RE-series manual also says the heater must be inspected annually by a trained and qualified professional, and that scale builds faster when the heater is set to a high temperature.

• Noritz says the cold water inlet filter should be checked about once a year, and that a unit on hard water with no softener will need an annual flush. For units without scale detection, Noritz suggests booking a checkup one year after installation. If your plumber finds significant scale, descale at least once a year. If not, you can go longer.

Why Lower Mainland water changes the answer

Metro Vancouver describes its drinking water as soft. Water from the Seymour-Capilano Filtration Plant averages about 20 mg/L of hardness, and water from the Coquitlam Water Treatment Plant averages about 2.5 mg/L. Both sit well inside the "soft" band in Navien's table.

Metro Vancouver also points out that soft water leaves less mineral buildup on household appliances. That doesn't mean you can skip maintenance. Rinnai still says to flush at least once a year, and your manual and warranty terms decide whether descaling stays on the list. A yearly visit also covers more than scale: the inlet filter, the venting, the burner and the relief valve all get checked (more on that below).

The rest of BC is more mixed. A fact sheet in BC's Water Stewardship Information Series says BC water generally ranges from under 10 to 180 mg/L, and that groundwater tends to be harder than surface water and can go above 1,000 mg/L. If your home is on a private well, test the water before you set a maintenance schedule. Don't assume the Interior is always hard, either: the City of Kamloops reported treated water hardness of around 40 mg/L in 2025, which is soft. Your municipality's annual water quality report will list the number for your system.

One tip for reading your manual: many give hardness in grains per gallon. Metro Vancouver says to divide mg/L by 17.1 to get grains per U.S. gallon.

What a full maintenance visit should cover

Going by the Rinnai, Noritz and Navien documents, a proper service on a tankless unit includes:

• Descaling the heat exchanger, if your water and your manual call for it.

• Cleaning the cold water inlet filter. It's a small screen where water enters the unit. Rinnai lists cleaning it as one fix when a heater keeps shutting off at low flow, because sediment there can reduce flow.

• Checking the venting. Rinnai's manual calls for checking the vent system and termination screens for blockages, including snow and debris. Noritz lists the front cover, fan and venting.

• Checking the burner. Rinnai says the flame should be clear, blue and stable, and the burner and fan should be kept free of dust.

• Testing the pressure relief valve. Rinnai says to operate it manually once a year.

Our tankless service and repair visits cover descaling, filter cleaning and system checks.

No service valves? That's the first fix

Flushing depends on isolation valves with service ports on the hot and cold lines under the heater. Rinnai strongly recommends installing them so the heat exchanger can be flushed. If your heater was installed without them, they have to be added before it can be flushed this way, and that's plumbing work.

Can you do it yourself?

Navien says a homeowner with the right equipment and some plumbing experience can descale a unit. It still recommends a professional, and warns that if descaling is done wrong and the heater is damaged, you could void the warranty. Rinnai says flushing should be done by a professional installer. Noritz says its maintenance procedures should be done by a trained service professional because the work involves gas, water and electricity in a tight space.

If you do it yourself, Rinnai's steps start by turning off the power, shutting off the gas and closing the water valves. It also warns that there may be pressure behind the purge port caps when you remove them, so make sure the hot water valve is fully closed first.

Signs it's due sooner

• A scale code on the display. On Rinnai units, an "LC" code means scale is building up in the heat exchanger and it needs a flush. Some Rinnai models also have a "Service Soon" reminder that can be set. Many Noritz models have scale detection that shows an error when it's time to descale.

• Less hot water flow or weaker performance than you're used to. Navien lists reduced flow and efficiency as effects of scale.

• The heater cutting out at low flow. Rinnai lists a dirty inlet filter as one possible cause.

If a code keeps coming back after a flush, or the heater won't fire at all, it's time for a repair visit rather than more vinegar.

The FortisBC rebate for tankless service

If you're a residential FortisBC natural gas customer, FortisBC offers a $50 rebate for servicing a tankless water heater, limited to one per household per calendar year. Storage tank water heaters aren't eligible. A few conditions from the program terms:

• The service has to be done by a contractor licensed by Technical Safety BC, and a visual inspection alone doesn't qualify. The work has to follow Technical Safety BC's complete service checklist.

• You apply online within 60 days of the service invoice. The invoice needs to describe the work and list the tankless heater's brand.

• The rebate comes as a credit on your gas bill, and applications can take up to 90 days to process.

The same program pays $50 for a furnace or boiler service, so it's worth booking both at once. Our post on how often to service a furnace or boiler in BC covers that side. FortisBC can change or end the program at any time, so check the current details before you book.

Book your tankless maintenance

Ark Plumbing & Heating's licensed plumbers and gasfitters service and repair tankless water heaters across the Lower Mainland. Still choosing a system? Read our tankless vs. tank comparison. If you're in Surrey, see our Surrey tankless service page. Call 604-441-3411 or send us a message to book a visit.