Why does my tankless water heater go hot and cold?

The cold-water sandwich usually means short draws, a failing flow sensor, mineral scale restricting flow, or a recirculation loop that needs attention. We test flow and ignition under real use.

How often should tankless units be descaled in San Jose?

Once a year is the right cadence for most San Jose homes given local water hardness. Recirculation systems may need it sooner. Missed descaling is the top cause of premature tankless failure here.

How much does tankless water heater repair cost in San Jose?

Tankless repair cost depends on the brand, error code, part involved, service history, venting, gas pressure, and whether the unit needs descaling or a component repair. Send photos of the error code, data plate, and install location for a faster phone estimate.

Do you repair Rinnai and Noritz tankless systems?

Yes. We service Navien, Rinnai, Noritz, Rheem, A.O. Smith, and Bradford White tankless units — both condensing and non-condensing.

Can you repair a tankless unit the same day?

Often, yes. Same-day repair depends on the error code, part availability, unit access, and whether the issue is scale, ignition, gas pressure, venting, condensate, or a failed component. We triage by phone and photos first when possible.

Is descaling enough or do I need a repair?

If the unit is under 8 years and hasn't been descaled in a year, descaling often clears flow and ignition errors. If symptoms persist after a proper flush, the next step is a component check.

When should I replace a tankless unit?

Replacement makes sense when the heat exchanger fails, when major component cost approaches a new unit, or when the unit is 12+ years old with declining performance.

Do you offer a warranty on tankless repairs?

Efficient Water Heaters provides a one-year labor warranty on qualifying tankless installation and replacement work. Warranty terms for repair parts and tankless service vary by brand, part, and service type. We document warranty terms before we leave the job.

San Jose Water Heater Specialist

Tankless Water Heater Repair in San Jose, CA

Specialist diagnostics and repair for Navien, Rinnai, and Noritz tankless units — error codes, ignition, flow issues, descaling, and venting.

Call (408) 470-0191 for Tankless Repair Get Phone Estimate

Licensed CSLB #1008381
Navien Service Specialist
Rinnai PRO
Noritz Certified
Error Code Diagnostics
Same-Day Service

Tankless water heater repair in San Jose by a licensed technician

What this service covers

Most tankless calls in San Jose trace back to mineral scale, ignition components, flow sensors, or venting. We diagnose by error code, then verify with flow, gas pressure, and combustion checks.

Navien E110, E003, E012, E016 error codes
Rinnai 11, 12, 14, 25, 79 error codes
Noritz 11, 12, 14, 90 error codes
Cold-water sandwich and inconsistent temperature
Mineral scale and flow restrictions
Ignition, flame rod, and burner failures
Condensate, vent, and combustion-air issues
Flow sensor and bypass valve repairs
Recirculation settings and pump issues

For Navien-specific service, see Navien tankless service.

How Our San Jose Tankless Repair Process Works

Read the error code and symptoms

We start with the display code, last service date, and what changed — flow drop, ignition fail, no hot water, or temp swings.

Check flow, ignition, venting, condensate, and scale

We verify gas pressure, flow rate, ignition, flame rod, condensate, and venting. Scale shows up fast on San Jose units.

Repair or descale the unit

We replace the failed component or perform a full descaling flush, depending on the actual cause.

Test operation and explain maintenance

We verify steady output, document the repair, and set a descaling cadence so the issue doesn't repeat.

What we do on the job

Tankless repair is technical. We use the manufacturer service manuals, not guesswork.

Read and clear error code history
Verify inlet/outlet gas pressure
Check flow sensor and bypass valve
Inspect flame rod and igniter
Test combustion and carbon monoxide safety where applicable
Verify condensate trap and neutralizer
Full descaling flush with isolation valves
Confirm vent length, slope, and termination

Tankless Review

“My new house had a tankless water heater without a descaling filter. Tried to call multiple places around but I did not get many responses back. Efficient Water Heaters had prompt and great communication, and I was able to book an appointment right away. Installation was done very quickly and professionally by Martin. I could not be happier!”

Y. W. — San Jose, CA

San Jose Tankless Factors We Check

San Jose water is moderately hard. In tankless systems across Willow Glen, Cambrian, Rose Garden, Almaden, Berryessa, Evergreen, Sunnyvale, and West San Jose, mineral scale is one of the most common causes of flow restriction, ignition errors, temperature swings, and premature heat-exchanger stress. We check the full system — not just the visible error code.

Hard-water scale on heat exchangers
Missed descaling intervals
Recirculation lines feeding scale back in
Condensate trap blockages
Venting length, slope, and termination
Gas pressure under simultaneous use
Power-vent and combustion-air clearances
Isolation valve access for future descaling

We service tankless units across San Jose, Santa Clara, Sunnyvale, Cupertino, Mountain View, Campbell, Los Gatos, Saratoga, Milpitas, and the South Bay.

Descale vs Repair Part vs Replace Unit

Tankless failures usually fall into three buckets. Use this matrix to decide which path fits.

Decision factor	Descale is enough	Repair a part	Replace the unit
Symptoms	Flow drop, intermittent ignition errors, mild temp swings	Specific component failure — flow sensor, flame rod, igniter, or gas valve — diagnosed by error code	Hard error code on heat exchanger or control board
Service history	No descaling in 12+ months, otherwise healthy unit	Descaled recently, one component is failing	Recently descaled and still failing, multiple repairs in past 12 months
Age	Any age with healthy heat exchanger	Under 10 years, heat exchanger sound	10+ years with failed heat exchanger or repeated failures
Repair cost vs unit cost	Lowest — descaling and minor part if needed	Mid — one component plus labor	Major component replacement approaches unit cost — better to replace
2027 BAAQMD planning	Keep current unit if safe, plan ahead for 2027 rules	Repair extends life past 2027 evaluation if zero-NOx-ready	Compare zero-NOx-ready replacement options before choosing

Symptoms

Descale is enough: Flow drop, intermittent ignition errors, mild temp swings

Repair a part: Specific component failure — flow sensor, flame rod, igniter, or gas valve — diagnosed by error code

Replace the unit: Hard error code on heat exchanger or control board

Service history

Descale is enough: No descaling in 12+ months, otherwise healthy unit

Repair a part: Descaled recently, one component is failing

Replace the unit: Recently descaled and still failing, multiple repairs in past 12 months

Age

Descale is enough: Any age with healthy heat exchanger

Repair a part: Under 10 years, heat exchanger sound

Replace the unit: 10+ years with failed heat exchanger or repeated failures

Repair cost vs unit cost

Descale is enough: Lowest — descaling and minor part if needed

Repair a part: Mid — one component plus labor

Replace the unit: Major component replacement approaches unit cost — better to replace

2027 BAAQMD planning

Descale is enough: Keep current unit if safe, plan ahead for 2027 rules

Repair a part: Repair extends life past 2027 evaluation if zero-NOx-ready

Replace the unit: Compare zero-NOx-ready replacement options before choosing

Not sure which path fits your situation?

Call (408) 470-0191 Get Phone Estimate

Tankless Brands We Service

We service Navien, Rinnai, Noritz, Rheem, A.O. Smith, and Bradford White tankless systems — condensing and non-condensing, natural gas and propane. We diagnose by model number, error code, fuel type, venting path, isolation-valve setup, condensate routing, and descaling history.

Get Phone Estimate

Send your details and a photo. We’ll respond fast during business hours.

Full name

Phone

City

Service needed

Describe the issue

Include the brand, model number, error code, symptoms, whether hot water starts then shuts off, when the unit was last descaled, and whether the issue affects one fixture or the whole home.

Upload photos (optional)Add photos of your water heater

Best photos: full tankless unit, data plate / model label, display or error code, venting, gas line, water connections, isolation valves, condensate line, and any leak or corrosion area. HEIC and multiple files supported.

No spam. No pressure. A specialist will review your request during business hours.

Prefer to call? (408) 470-0191· 6 AM–10 PM, 7 days

Speak with a specialist

Phone estimates available during business hours.

(408) 470-0191

Open 24/7

Licensed CSLB #1008381 • Bonded & Insured

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Related guides & services

Frequently asked questions

E003 is ignition failure, E012 is flame loss, E016 is over-temperature, and E110 is intake or exhaust blockage. We diagnose the root cause — gas, ignition, venting, or scale — rather than just clearing the code.

Tankless Error Code or No Hot Water? Call Now.

Call or request a phone estimate. Send the error code and a photo of the data plate — we'll often narrow the likely repair before we roll a truck.

Call (408) 470-0191 Get Phone Estimate

Licensed CSLB #1008381
Bonded & Insured
Open 24/7

Navien Service Specialist · Rinnai PRO · Noritz Certified