A tankless water heater is one of the best investments in a GTA home. It never runs out of hot water, uses significantly less energy than a tank, and lasts 20–25 years when properly maintained. That last part is the catch: properly maintained. A tankless unit that goes years without service quietly loses efficiency, and by the time the problem is obvious, it is either running at a fraction of its rated capacity or triggering fault codes that shut it down entirely.
This guide explains what tankless water heater service involves, how often it needs to happen, and what the warning signs of a neglected unit look like.
Quick answer
- How often: once a year in the GTA, because of scale from Lake Ontario water.
- What is done: heat exchanger descale (45–60 minute circulation), inlet filter clean, condensate drain check, vent check, error-code review.
- Typical cost: $150–$250 for the descale, against $800–$1,500 for a heat exchanger replacement.
- Do it yourself? The descale is not a DIY job. The checks below are safe to do before you call.
Why Tankless Water Heaters Need Annual Service in the GTA
The core problem is water hardness. The Greater Toronto Area and York Region are served by Lake Ontario source water that, after treatment, still contains enough dissolved calcium and magnesium to cause progressive scale buildup inside any appliance that heats water. The effect on a tankless water heater is specific and measurable: calcium carbonate deposits on the heat exchanger coils reduce heat transfer efficiency year over year. A unit that is running 20% below its rated output — entirely because of scale — feels like low water pressure or inconsistent hot water temperature, but the root cause is a heat exchanger that cannot deliver the same BTU transfer it could when it was new.
The harder the water, the faster the scale accumulates. In York Region communities including Richmond Hill, Vaughan, Markham, and Newmarket, the water hardness is high enough that annual descaling is not optional maintenance — it is what keeps the unit within its rated specifications.
What a Tankless Water Heater Service Includes
1. Heat Exchanger Descaling (the core service)
The heat exchanger is flushed with a diluted descaling solution — typically food-grade citric acid or a commercially formulated descaler — circulated through the coils for 45–60 minutes to dissolve calcium carbonate deposits. The flush removes the scale layer, restores heat transfer efficiency, and prevents the progressive narrowing of flow passages that eventually causes low pressure and fault shutdowns.
This is not a DIY service. It requires isolating the unit from the supply line, using a submersible pump to circulate the descaling solution, and confirming the unit’s recovery before restoring supply. Doing it incorrectly — using the wrong descaler, insufficient circulation time, or failing to neutralise and flush completely — can damage the heat exchanger rather than clean it.
2. Inlet Water Filter Cleaning
Most tankless water heaters have a small mesh filter on the cold water inlet connection. Over time, sediment, mineral particles, and debris from the supply line collect on this screen and restrict incoming water flow. A clogged inlet filter is one of the most common causes of apparent “low pressure” from a tankless unit — and one of the easiest to fix. We remove and clean or replace the filter screen at every service.
3. Condensate Drain Inspection (condensing units)
High-efficiency condensing tankless units produce acidic condensate as a byproduct of combustion. That condensate is routed to a drain through a small plastic trap and drain line. If the trap becomes blocked — with mineral deposits, debris, or a biological buildup — the unit triggers a safety shutdown. This is a common mystery fault that presents as the unit unexpectedly cutting out during use. Clearing the condensate drain is part of every service on condensing units.
4. Air Intake and Exhaust Inspection
Tankless water heaters draw combustion air and vent exhaust through one or two plastic pipes that run to the exterior of the building. Bugs, birds, and debris can partially block these vents, which affects combustion efficiency and can trigger safety codes. We visually inspect both the intake and exhaust terminations at every service call.
5. Error Code Review
Most modern tankless units maintain an error log. We pull the stored fault codes and review them even if the unit is currently running normally — intermittent faults that have not yet caused a shutdown are often predictors of the failure mode coming next. Catching a recurring fault code during a service visit is far better than catching it when there is no hot water.
How Often Does a Tankless Water Heater Need Servicing?
In GTA and York Region conditions: annually. This is consistent with every major manufacturer’s warranty requirements for areas with moderate to hard water.
Some installers and manufacturers say “every two years” in a general context. That interval is appropriate for areas with very soft water — not for the GTA. Waiting two years between descaling services in York Region water conditions allows enough scale to accumulate that efficiency drops measurably between service visits.
One practical test: if you run a tankless service call and the descaling flush returns heavily cloudy or white-tinged water during circulation, the unit was running significantly below capacity due to scale. Annual service prevents that degree of buildup.
Signs Your Tankless Water Heater Needs Service
- Hot water temperature fluctuates. Water comes out hot, then briefly lukewarm, then hot again. This is often the heat exchanger struggling to maintain consistent output through partially blocked flow passages.
- Lower flow than before. The shower pressure at full hot feels weaker than it used to. A clogged inlet filter reduces flow at the unit’s inlet; a heavily scaled heat exchanger restricts internal flow.
- Error codes on the display. Units from Navien, Rinnai, Noritz, and Bradford White all display fault codes on the front panel or connected app. If your unit is showing any code, do not ignore it.
- Unit cycles off mid-shower. This is a classic condensate drain blockage symptom — the unit reaches a drainage fault threshold and shuts down as a safety measure.
- Energy bill has increased without a corresponding change in usage. A scaled heat exchanger forces the burner to work harder to achieve the same output temperature. The unit uses more gas to deliver the same hot water.
What Happens If You Don’t Service a Tankless Unit
In the first two or three years without service: efficiency loss. The unit still works, just uses more gas than it should.
By year four or five without service: visible performance issues. Temperature fluctuation, lower flow, occasional fault codes.
By year seven or eight without service in hard water conditions: heat exchanger damage. Scale does not just coat the coils — in severe cases it chemically reacts with the heat exchanger metal and causes pitting and micro-fractures. At this stage, the heat exchanger may need replacement rather than just cleaning — an expensive repair that voids the case for keeping the unit at all.
Annual descaling costs $150–$250. Heat exchanger replacement costs $800–$1,500 if the unit is even worth repairing. The math is straightforward.
What You Can Check Yourself Before You Call
Some tankless problems are not scale at all. These checks take a few minutes and need no tools. Switch the unit off at its power button first, and stop if anything smells like gas: leave the house and call your gas utility.
- Read the display. Write down the exact fault code and what the unit was doing when it appeared. It tells us whether we are looking at scale, a blocked drain or a vent problem before we arrive.
- Look at the vent terminations outside. In a Toronto winter, snow, ice or a bird nest over the intake or exhaust pipe is a common reason a unit shuts down. Clear loose snow by hand; do not poke anything into the pipe.
- Check the condensate hose (condensing units). Look for a kink, a sag that holds water, or a hose that has slipped out of the drain.
- Check that the shut-off valves are fully open. A cold water valve left partly closed after other work mimics a scaled heat exchanger.
- Look for service valves on the water lines. Units installed with them are quicker and cheaper to descale. If yours has none, tell us when you book, because we will need to fit them.
If the code returns after you have cleared the vents and opened the valves, the cause is inside the unit and it needs a service call.
What to Have Ready When You Book
- The brand and model number, printed on the label on the side or bottom of the unit.
- Any fault code shown, and how often it appears.
- The date of the last service, if you know it. If it has never been serviced, say so; that is useful, not embarrassing.
- Whether you have a water softener or filter on the main line.
Tankless Water Heater Brands We Service
We service and repair all major tankless brands installed in GTA homes, including Navien, Rinnai, Noritz, Bradford White, A.O. Smith, Rheem, and Bosch. We carry common parts for the most frequently serviced models on every truck. For Navien units specifically — the most widely installed brand in new GTA construction since 2015 — we are familiar with the full fault code library and common failure modes.
Tankless Water Heater Service: Common Questions
Can I descale my tankless water heater myself?
We do not recommend it. The job needs the unit isolated from the supply, a pump to circulate the descaler for 45–60 minutes, and a full neutralise-and-flush afterwards. The wrong descaler or an incomplete flush can damage the heat exchanger instead of cleaning it.
Will skipping service affect my warranty?
Many manufacturers write maintenance requirements into the warranty for areas with moderate to hard water. Read the warranty section of your manual, and keep the service record we leave with you as proof the work was done.
Does a water softener mean I can skip the annual service?
A softener slows scale buildup, which helps, but it does not remove the inlet filter, condensate drain or vent checks. Units on softened water may go longer between descales; have the unit inspected once a year and let the result decide.
Does service differ for condensing and non-condensing units?
The descale, inlet filter and error-code review are the same. The condensate drain check applies only to condensing (high-efficiency) units, because only they produce acidic condensate.
How do I know it is scale and not a failing unit?
Scale builds gradually: hot water takes longer, temperature swings, flow drops over months. A sudden shutdown or a fault code that appears at once points to the drain, vent or a failed part. If the unit is also 15 or more years old, see our guide on signs a water heater needs replacing before paying for repairs.
Book Tankless Service With ED Plumbing
Our tankless service calls are booked as flat-rate appointments — the price we quote is the price you pay. We arrive with the descaling pump and solution, complete the full service in one visit, and leave you with a documented service record.
We service GTA-wide: Toronto, North York, Scarborough, Etobicoke, Vaughan, Richmond Hill, Markham, Mississauga, and all surrounding communities. Call (437) 260-6342 or book online. For units showing active fault codes, we prioritise same-day dispatch; with no hot water at all, use our emergency plumbing service.