Tankless Water Heater Leaking

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By Emergency Water Heater SLC Team · · Updated March 7, 2026 · 8 min read

It’s mid-morning, and you notice water pooling under your tankless unit. The question isn’t whether to panic—it’s whether you’re looking at a quick fix or a replacement scenario. Here’s what determines the answer.

Quick Answer

A leaking tankless water heater needs immediate diagnosis. Most leaks come from loose connections (fixable, $0–$100), hard water scale corrosion (professional descaling, $150–$300), or faulty pressure relief valves (replacement, $150–$300). Serious leaks from the heat exchanger cost $600–$1,300 to repair. Catch the leak early: water pooling under a wall-mounted unit can damage drywall and electrical connections. Turn off the water supply immediately and call a plumber (same day if possible). Repair costs range $270–$1,705 (as of March 2026); most small leaks stay under $500.

Symptoms and What They Mean

Water dripping slowly from the drain line (bottom of unit):
This is often normal. Tankless units produce condensation, especially in winter or during high demand. A steady drip every few seconds is acceptable. If it becomes a stream, the pressure relief valve may be stuck or the heat exchanger may be leaking internally—call a plumber.

Water pooling on the floor or wall beneath the unit:
This indicates an active leak from connections, internal corrosion, or the relief valve discharge. This requires professional attention same-day.

Water spraying or squirting from connection points:
High-pressure system failure or severely loose fitting. Turn off the water immediately and call a plumber. Do not attempt to tighten while water is pressurized.

Hissing sound from the unit, then water leaking:
The unit may be pressure-locked (dangerously high internal pressure). Do not approach it. Turn off the gas or electric, turn off the water supply, and call a plumber immediately.

Rust-colored water or staining around the unit:
Corrosion inside the heat exchanger. This indicates internal deterioration and typically requires replacement or major repair ($600–$1,300). Call a professional.

Safe Checks You Can Do Yourself

Step 1: Locate the leak source.
Is water coming from the pressure relief valve drain line (expected in some cases), connection fittings, or the unit body itself? Use a flashlight to look closely. Place a paper towel under the suspected area to pinpoint the source.

Step 2: Check for loose connections.
With the water heater still on, look for dripping at the inlet, outlet, and gas/electric supply connections. If you see a slow drip from a brass fitting, it may be loose. With the unit OFF and cool, use a wrench to gently tighten connection nuts (don’t over-tighten—snug is enough). Turn the unit back on and recheck.

Step 3: Inspect the pressure relief valve drain line.
The small copper or plastic line at the bottom of the unit is the PRV drain. It’s normal for this to drip slightly during high demand or cold weather (condensation). If it’s dripping steadily into a bucket-sized puddle within an hour, the PRV is leaking—call a plumber.

Step 4: Check the water supply valve.
Make sure the supply valve below the unit is fully open. A partially closed valve can cause pressure buildup and leaks. If you turn it, do so slowly and gently.

Step 5: Look for scale buildup around connections.
In Utah’s hard water (150–250 GPG), white or tan mineral deposits around fittings indicate scale corrosion starting inside. This doesn’t always cause leaks immediately, but it’s a warning sign. Note it for your plumber.

Do NOT attempt to take apart the unit or replace internal components yourself. Tankless systems are pressurized and complex—improper reassembly can cause gas or electrical hazards.

When This Becomes Dangerous

Stop here and call 911 if:

  • You smell gas and see water spraying from the unit simultaneously
  • The unit is making a loud hissing or siren sound
  • Water is spraying onto electrical outlets, the breaker panel, or visible wiring
  • You see flames, smoke, or an unusual burning smell

Call a plumber today (not tomorrow) if:

  • Water is actively pooling on the floor or dripping onto drywall
  • The leak started after you heard a loud pop or pressure release
  • You see rust-colored water or brown staining inside the unit
  • The unit was installed in an unheated garage or space, and it’s winter (freeze damage risk escalates quickly)

Monitor closely if:

  • You found and tightened a loose connection, but the leak resumes within 24 hours
  • The PRV drain line is dripping more than usual
  • You notice water in unexpected places (inside cabinets, inside walls if unit is recessed)

Tankless units are pressurized to 60–80 PSI. A sudden failure can spray water forcefully and damage adjacent components. Don’t ignore a leak hoping it will resolve.

What a Technician Will Check and Do

A plumber trained in tankless systems will:

  1. Diagnose the leak source — Visual inspection, pressure testing, and flow checks to pinpoint where water is escaping
  2. Assess corrosion level — If hard water scale is present, decide between descaling (cleaning) or component replacement
  3. Check pressure relief valve function — Replace if faulty ($150–$300 including labor)
  4. Test gas/electrical safety — For gas units, verify combustion is complete; for electric, check element integrity
  5. Perform descaling if needed — Flush the heat exchanger with citric acid or vinegar solution to remove mineral buildup ($150–$300)
  6. Replace faulty components — Valves, gaskets, or internal seals as needed
  7. Pressure test the entire system — Ensure the repair holds under normal operating pressure

For serious leaks (heat exchanger failure), replacement may be more cost-effective than repair, especially if the unit is 10+ years old.

Typical Repair Cost (as of March 2026)

IssueRepair TypeCost
Loose connection (re-tightened)DIY or 15-min service call$0–$75
Faulty pressure relief valveValve replacement + labor$150–$300
Hard water scale in heat exchangerProfessional descaling$150–$300
Worn gasket/sealComponent replacement + labor$200–$400
Corroded internal pipingHeat exchanger replacement$600–$1,300
Multiple component failureFull overhaul or replacement$1,300–$2,500

Labor rate: $150–$200/hour in Utah (Wasatch Front)

Service call: $75–$150 (often credited toward repair if work is performed same day)

Prevention: Utah-Specific Hard Water & Freeze Protection

Hard water maintenance: Utah’s 150–250 GPG hardness causes mineral scale inside tankless heat exchangers. Scale buildup causes corrosion and leaks. Professional descaling every 1–2 years (or annually in very hard water areas) prevents failures. Cost: $150–$300 annually prevents $600+ repairs.

Freeze protection: Tankless units in unheated Utah garages are vulnerable to freeze damage. If pipes freeze, the unit can crack internally when water thaws. Insulate the unit, drain the lines before winter, or use a freeze-protection valve (asks technician about options for your specific model).

Annual maintenance: Have a technician inspect annually (spring, after winter). They’ll check for scale, pressure, gas flow, and venting. Cost: $100–$150 per visit, but catches problems before they cause leaks.

Find Local Help

Tankless water heater repairs require specialized knowledge. Don’t trust a general plumber without tankless experience—improper repairs can create safety hazards. Find a contractor certified in your unit’s brand (Rinnai, Navien, Takagi, etc.).

FAQ

Q: Is a drip from the pressure relief valve normal?
A: A slow drip (1–2 drops per minute) during high-demand periods (winter showers) is normal and indicates the PRV is working. If it becomes a steady stream or happens constantly, the PRV is faulty and needs replacement.

Q: Can I repair a tankless water heater myself?
A: Tightening a loose fitting is DIY-safe. Descaling or replacing internal components requires professional training. Improper reassembly can cause gas/electrical hazards or water damage. Leave internal repairs to certified technicians.

Q: My tankless heater is leaking. Should I replace it?
A: Not necessarily. If the unit is under 10 years old and the leak is minor (valve, seal, or scale), repair is cost-effective. If it’s 12+ years old with a major heat exchanger leak, replacement may be smarter. A technician can advise.

Q: How do I prevent hard water leaks in Utah?
A: Descale annually (professional or DIY with citric acid kits). Install a water softener if you’re staying long-term (ROI: 5–7 years). Ensure proper maintenance per your unit’s manual.

Q: What if water damage occurred from the leak?
A: Document photos, call your homeowner’s insurance, and get written repair estimates. Most policies cover sudden water damage. Water heater leak repairs may be covered depending on your deductible and coverage type.

Q: Can I use a water heater leak detection and auto-shutoff system?
A: Yes. Systems like FloodMaster or Watts LFWDS detect water under the heater and automatically shut off the supply, preventing major water damage. Cost: $150–$300 installed. Worth considering if your unit is in a space with valuable items below (basement, closets).

Q: My tankless heater is in an unheated Utah garage. How do I prevent freeze damage?
A: Drain the lines before winter, insulate the unit with a blanket or box, and ensure the garage doesn’t drop below 32°F (use a space heater if needed). Check your unit’s manual for freeze-protection valve options. A preventative check costs $75–$150; freeze damage replacement costs $2,000–$4,000.

Sources and Update Policy

This article references repair costs and techniques current as of March 2026. Pricing may vary by region and contractor expertise. Always get a written estimate before authorizing repairs.

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