Tankless water heaters have become increasingly popular in Philadelphia homes — and for good reason. They deliver hot water on demand, take up far less space than traditional tanks, and can last 20 years or more. But here's the catch that many homeowners don't realize: tankless units are not maintenance-free. In fact, neglecting annual maintenance on a tankless water heater can shorten its lifespan dramatically, reduce efficiency, and void your manufacturer's warranty.
Whether you recently installed a tankless unit or you've had one for years, here's everything you need to know about keeping it in peak condition — especially in the Philadelphia area, where our water quality plays a big role.
Why Tankless Water Heaters Need Regular Maintenance
Unlike traditional tank water heaters that store and continuously heat a reservoir of water, tankless units heat water as it flows through a heat exchanger. That heat exchanger is the heart of the system — and it's vulnerable to mineral buildup, especially in areas with hard or moderately hard water like much of the Greater Philadelphia region.
Philadelphia's municipal water, supplied by the Philadelphia Water Department, is considered moderately hard at roughly 100–150 mg/L of calcium carbonate. Homes in Delaware County, Montgomery County, and the Main Line that draw from different sources may have varying hardness levels. Over time, calcium and magnesium deposits accumulate inside the heat exchanger, creating scale that:
- Reduces heat transfer efficiency (higher energy bills)
- Forces the unit to work harder, increasing wear on components
- Restricts water flow, causing temperature fluctuations
- Can trigger error codes that shut the unit down entirely
The Annual Flush: The Most Important Maintenance Task
The cornerstone of tankless water heater maintenance is an annual descaling flush. This process involves circulating a food-grade descaling solution (typically white vinegar or a commercial descaler) through the heat exchanger to dissolve mineral buildup. Here's what's involved:
- Shut off the gas or electrical supply to the unit and close the incoming water valves.
- Connect a submersible pump to the service valves (most tankless units have dedicated flush ports).
- Circulate the descaling solution through the heat exchanger for 45–60 minutes.
- Flush with clean water to remove any remaining solution and loosened scale.
- Clean the inlet water filter — a small screen that catches sediment before it enters the unit.
- Restore gas/electric and water supply, then test the unit for proper operation.
Can You DIY a Tankless Flush?
Some handy homeowners do flush their own tankless water heaters using a pump kit (available at most hardware stores for $100–$150). However, there are good reasons to have a professional handle it: a trained technician will also inspect the burner assembly (on gas units), check the venting system for obstructions or corrosion, test the pressure relief valve, and verify that all components are operating within manufacturer specifications. Many warranty programs require documented professional maintenance to remain valid.
Beyond the Flush: Other Maintenance Tasks
While descaling is the headliner, a complete tankless water heater service includes several additional checks:
Inlet Filter Cleaning
Every tankless unit has a small mesh filter on the cold water inlet. In Philadelphia's older neighborhoods — Germantown, Fishtown, South Philly — where aging municipal pipes can introduce sediment, this filter can clog faster than you'd expect. Cleaning it takes just a few minutes but prevents flow restrictions that cause the unit to underperform or display error codes.
Venting Inspection (Gas Units)
Gas-fired tankless water heaters require proper venting to exhaust combustion gases safely. During maintenance, the technician checks for obstructions (bird nests are surprisingly common in Philadelphia), corrosion, loose connections, and proper slope. Improper venting is a carbon monoxide risk — this isn't something to skip.
Burner and Flame Rod Inspection
The burner assembly and flame rod (ignition sensor) should be visually inspected and cleaned if needed. A dirty flame rod is one of the most common causes of ignition failure in gas tankless units. The fix is simple — a quick cleaning with fine sandpaper — but diagnosing the problem without experience can be frustrating.
Pressure Relief Valve Test
Like tank water heaters, tankless units have a temperature and pressure (T&P) relief valve. This safety device should be tested annually to ensure it opens and reseals properly. A failed T&P valve is a safety hazard that should be replaced immediately.
How Philadelphia's Water Quality Affects Maintenance Frequency
The general recommendation is annual maintenance, but your specific situation may call for more or less frequent service:
- Hard water (no water softener): Consider flushing every 6–9 months. This is especially relevant for homes in parts of Chester County and Montgomery County where well water can be quite hard.
- Softened water: Annual flushing is typically sufficient, and scale buildup will be minimal.
- High usage households: Families of four or more, or homes with multiple bathrooms running simultaneously, should stick to annual service at minimum.
- Vacation homes or low usage: Even if you don't use the unit heavily, annual maintenance prevents problems from sitting water and ensures components stay functional.
Signs Your Tankless Water Heater Needs Service Now
Don't wait for your annual appointment if you notice any of these warning signs:
- Fluctuating water temperature — hot water that goes cold and back to hot (the dreaded "cold water sandwich")
- Reduced hot water flow — lower pressure at the tap than usual
- Error codes on the display panel — most units display specific fault codes
- Strange noises — clicking, humming, or rumbling from the unit
- Higher energy bills — a scaled-up heat exchanger uses more gas or electricity to achieve the same output
- Visible scale or discoloration at the hot water outlets
The Cost of Maintenance vs. the Cost of Neglect
A professional tankless water heater flush and inspection typically costs between $150 and $250 in the Philadelphia area — a modest investment considering the alternative. A neglected heat exchanger can fail prematurely, and replacing one runs $500–$1,500 depending on the brand and model. In severe cases, the entire unit may need replacement years ahead of schedule — turning what should have been a 20-year investment into a 10-year one.
There's also the warranty angle. Most major manufacturers — Navien, Rinnai, Noritz, Rheem — require annual professional maintenance to honor their warranties. Skip it, and a $1,200 heat exchanger replacement that should have been covered becomes your out-of-pocket expense.
GenServ Pro's Home Shield Plan Covers This
Our Home Shield maintenance plan includes annual water heater service — tankless or traditional — along with HVAC tune-ups and plumbing inspections. It's the easiest way to stay on top of maintenance without having to remember to schedule it yourself. Plus, Home Shield members get priority scheduling and discounts on repairs.
Choosing the Right Professional for Tankless Maintenance
Not all plumbers are experienced with tankless water heaters. When selecting a service provider in the Philadelphia area, look for:
- A valid PA Home Improvement Contractor (HIC) license
- Specific experience with your brand of tankless unit
- Manufacturer certification (many brands offer training programs)
- Transparent pricing — you should know the cost before work begins
- A thorough service that includes descaling and component inspection, not just a quick flush
GenServ Pro's plumbing technicians are trained on all major tankless brands and carry the necessary flush equipment on every service call. We serve Philadelphia, the Main Line, Delaware County, and surrounding communities — and we'll always explain what we found and what we recommend before performing any additional work.
Keep Your Tankless Water Heater Running Like New
Whether it's time for your annual flush or you're noticing warning signs, GenServ Pro is here to help. Licensed, insured, and 4.9-star rated across Philadelphia and the Main Line.