Quick answer
Tankless water heater maintenance costs $150–$300 for an annual descale flush on a unit that has isolation valves. That visit covers the descale, the inlet filter screen, flame rod and igniter cleaning, the condensate neutraliser and a combustion check. The price rises when there are no service valves, when scale is heavy after years without a flush, or when the visit turns up a repair.
Tankless water heater maintenance costs $150–$300 a year around Burlington, Hamilton and the west GTA when the job is a routine descale flush. That figure assumes the unit was installed with isolation valves and has been flushed within the last year or two. A unit that is already throwing an error code or going cold mid-shower is a repair call, and it is priced as one.
What a tankless service visit costs in Ontario
- Annual descale flush with filter and burner-side cleaning: $150–$300.
- Diagnostic visit for a unit showing a fault code: $90–$150, folded into the repair if you go ahead.
- Repairs found during the service, such as a worn flame rod or igniter: most water heater repairs run $150–$800, quoted in writing before the part goes in.
- Adding isolation valves to a unit that was installed without them: a written quote, because the price depends on the piping in front of the heater.
The full list of published bands is on the pricing page. If the unit has stopped working instead of just being overdue, read what tankless water heater repair costs first, because the numbers are different.
What a technician does during a tankless flush and service
- Descale through the isolation valves: the unit is valved off from the house, hoses and a small pump are connected to the service ports, and white vinegar or a citric acid descaler is circulated through the heat exchanger for roughly 45 to 60 minutes, then rinsed out with clean water.
- Inlet filter screen: the small mesh screen on the cold-water inlet is pulled and rinsed. Grit packed into it is a common cause of weak flow and water that swings hot and cold.
- Flame rod and igniter: the flame rod proves to the control board that the burner is lit. An oxide film on it makes a healthy flame look like no flame, and the unit lights, drops out and locks on a code.
- Condensate neutraliser: on condensing models the acidic condensate runs through a cartridge of neutralising media before it reaches the drain. The media is used up over time and the trap can plug, which shuts the heater down.
- Combustion check: gas pressure is measured with the burner firing and the flue gas is read with an analyser, alongside a look at the air intake screen, the vent joints and the stored error history.
Why the price changes from one house to the next
The biggest swing is whether isolation valves were installed. They are the pair of service valves with hose ports under the unit, and without them there is no way to loop descaler through the heat exchanger without cutting into the piping. A valve kit has to go in first, which turns a flush into a small plumbing job.
- Heavy scale: municipal water in Halton and Hamilton is hard, and private wells in rural Caledon, Kilbride, Campbellville and Carlisle are often harder. A heat exchanger that is badly limed needs a longer circulation, sometimes a second batch of descaler.
- No water softener: softened water leaves far less scale behind, so the flush is quick. Unsoftened hard water is where the long visits come from.
- Years since the last flush: a unit serviced every year takes one routine visit. One that has gone five years may flush clean, or the flush may reveal an exchanger that is already restricted.
- Condensing or non-condensing: a condensing unit has a trap and neutraliser to service that a non-condensing one does not.
How often a tankless needs service on Halton and Hamilton water
Once a year on unsoftened hard water. With a working softener the interval can stretch, and what comes out during the flush tells the technician how far. Signs that a unit is overdue are covered in how to tell if a tankless needs descaling.
There is a warranty reason as well. Navien, Rinnai and Noritz all write water-quality conditions into their warranties, and a heat exchanger claim can be denied when the failure is scale damage. Keep the dated service invoices with the installation paperwork; they are the proof that the flushes were done.
Can you descale a tankless water heater yourself?
The water side, yes, if the isolation valves are there: a pump, two hoses, a bucket and vinegar will do it, and the owner's manual gives the steps. The burner side is different. Cleaning the flame rod and igniter, measuring gas pressure and reading combustion are work for a TSSA-licensed gas technician, and they are the half of the service that catches a problem before it becomes a lockout.
ZK Mechanical services Navien, Rinnai and Bosch units across Burlington, Oakville, Milton, Hamilton and Mississauga, with the price confirmed in writing before the pump is connected. If the flush turns up a fault, the same technician handles the tankless water heater repair. Call (647) 801-1252 or book a service visit, and see the water heater answers hub for related questions.