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Hard Water Scale Removal & Tankless Flushing — A San Jose Guide

Santa Clara Valley water is hard. That mineral load is the single biggest reason tankless water heaters in this area lose flow, throw overheat codes, and die early. Here is exactly what scale does, how flushing removes it, and how to know when it has gone too far.

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Open 24/7 · CSLB #1008381 · Joseph J. Castro, Owner · contact@efficientwaterheaterssanjose.com

Hard Water Scale Removal & Tankless Flushing — A San Jose Guide

Quick answer

Hard water leaves calcium and magnesium scale on the inside of a tankless heat exchanger. In San Jose, where water typically runs 10 to 20 grains per gallon, that scale builds fast enough to cause temperature swings, reduced flow, and E016 or E030 overheat codes within a year or two. Removing it means circulating a food-grade descaling solution through the unit for 45 to 60 minutes using the isolation valves, then rinsing with clean water. Most homes need this once a year; harder-water areas like Morgan Hill and Gilroy often need it every 6 to 9 months. Efficient Water Heaters, Inc. performs professional descaling 24/7 at (408) 470-0191, CSLB #1008381.

What hard water actually does inside a tankless unit

A tankless heat exchanger pushes water through narrow copper or stainless passages against a burner running up to 199,900 BTU. Dissolved calcium and magnesium come out of solution at those surface temperatures and bond to the walls as hard, chalky scale.

  • Scale insulates the exchanger, so the burner runs hotter to hit the same outlet temperature
  • Narrowed passages cut flow — the shower that used to run 4 GPM now sputters at 2.5
  • Hot spots trigger the unit's safety limits, which is where E016 and E030 overheat codes come from
  • Long term, thermal stress from hot spots cracks the exchanger — the most expensive part of the unit
  • Efficiency drops measurably: a scaled unit burns more gas for the same hot water

How hard is South Bay water, really

Hardness across our service area lands in the moderately-hard to very-hard range, and it varies by source and by season. What matters is that it is hard enough, everywhere we work, to scale a tankless unit that is never flushed.

  • San Jose, Santa Clara, Milpitas, Sunnyvale: hard enough for a firm annual descaling schedule
  • Cupertino, Saratoga, Los Gatos, Monte Sereno: hard water plus long recirculation runtime — often 9 months
  • Morgan Hill, San Martin, Gilroy: the hardest water we work with, frequently well-fed; 6 to 9 months is realistic
  • Peninsula cities: a somewhat gentler supply, but older plumbing adds variables the flush visit uncovers
How hard is South Bay water, really

Warning signs your heat exchanger is already scaled

Scale rarely announces itself all at once. It shows up as small annoyances first, then as fault codes, then as a failed unit. Catching it at the annoyance stage is the difference between a flush and a replacement.

  • Hot water that swings warm to cold during a steady shower
  • Lower flow at the hot tap than the cold tap at the same fixture
  • The burner cycling on and off more often than it used to
  • E016, E030, or repeated overheat-family codes on the display
  • A rattling or kettling sound from the unit while it fires
  • Higher gas usage with no change in household habits

Flushing vs descaling vs a full maintenance visit

These three terms get used interchangeably online, and they are not the same job. Knowing the difference keeps you from paying for the wrong service — or from thinking you are protected when you are not.

  • Flushing: circulating water to clear loose sediment and debris. Helpful, but it will not remove bonded scale.
  • Descaling: circulating a food-grade acidic solution for 45 to 60 minutes to dissolve hardened calcium. This is the job that restores the exchanger.
  • Full maintenance: descaling plus inlet screen cleaning, air filter service, flame rod and igniter inspection, venting and condensate check, gas pressure test under load, and outlet temperature verification.

Prevention: softeners, scale inhibitors, and isolation valves

Descaling is treatment. Slowing how fast scale forms in the first place is prevention, and in the hardest parts of our service area it pays for itself.

  • Whole-home softener: the most effective option in Morgan Hill, San Martin, and Gilroy
  • Template-assisted crystallization or scale-inhibitor cartridges: no salt, no discharge, moderate protection
  • Isolation service valves: not prevention, but without them every future descaling costs more because pipe has to be cut
  • Setting the outlet temperature no higher than needed — hotter surfaces precipitate scale faster
  • Keeping annual service records, which Navien expects if you ever file a warranty claim

When DIY stops and a licensed pro starts

A careful homeowner with isolation valves, a pump, and a few hours can do a descaling. Some situations are not DIY, and forcing them usually costs more than the service call would have.

  • No isolation valves installed — the unit must be re-piped before it can be flushed
  • The unit still throws an overheat code after a full descaling
  • Any gas smell, water leak at the unit, or scorching around the vent
  • Commercial or cascade systems, where one unit offline affects the whole building
  • A unit still under Navien warranty, where documented professional service protects your coverage

How to flush and descale a tankless water heater in a hard-water area

This is the sequence we follow on a residential descaling visit in San Jose. Work only on a unit that has isolation service valves. If you smell gas, see a leak, or are unsure at any step, stop and call a licensed contractor.

What you need: Submersible utility pump, Two washing-machine hoses, 5-gallon bucket, Adjustable wrench, 4 gallons of white vinegar or a food-grade descaling solution, Replacement inlet filter screen gasket if the old one is worn, Clean rinse water

  1. Shut down the unit safely

    Turn off the gas supply valve to the unit and cut power at the switch or breaker. Let the unit cool for 20 to 30 minutes before touching any plumbing — the exchanger holds heat well past shutdown.

  2. Close the isolation valves and relieve pressure

    Close the hot and cold isolation valves so the unit is separated from house plumbing. Open the service port caps slowly with a bucket underneath to relieve pressure and drain the water inside the exchanger.

  3. Connect the pump and hoses

    Run one hose from the pump in the bucket to the cold service port and a return hose from the hot service port back into the bucket. Fill the bucket with about 4 gallons of white vinegar or descaling solution, then open both service port valves.

  4. Circulate the descaling solution

    Run the pump for 45 to 60 minutes. In hard-water areas like Morgan Hill or Gilroy, or on a unit that has never been serviced, go the full hour. The solution should darken and carry loose flakes as bonded scale releases.

  5. Clean the inlet filter screen

    While the solution circulates, remove the cold-water inlet filter screen and rinse the trapped grit out of it. Inspect the gasket, replace it if it is flattened or cracked, then reinstall the screen snugly.

  6. Rinse with clean water

    Stop the pump, dump the used solution, and refill the bucket with clean water. Circulate for 5 to 10 minutes so no acidic residue stays in the exchanger. Remove the hoses and reinstall the service port caps.

  7. Restore service and verify performance

    Open the isolation valves, open the gas valve, and restore power. Run a hot tap for two minutes and confirm a steady outlet temperature, full flow, and no error code on the display. Write down the date so your maintenance record stays current.

Hard water and flushing intervals across the areas we serve

We descale tankless systems throughout Santa Clara County and the mid-Peninsula, and we do not recommend the same interval everywhere because the water is not the same everywhere. San Jose, Santa Clara, Sunnyvale, and Milpitas homes usually do well on a clean annual cycle. Cupertino, Saratoga, Los Gatos, Monte Sereno, and Los Altos combine hard water with long hot-water runs and recirculation, which pushes service closer to nine months. Mountain View, Palo Alto, Menlo Park, East Palo Alto, Redwood City, Atherton, Portola Valley, and Woodside sit on Peninsula supply where older plumbing adds its own variables. Morgan Hill, San Martin, and Gilroy have the hardest water in our footprint, and well-served properties there commonly need descaling twice as often as a San Jose townhome.

Pick your city below for local water detail, or call and we will tell you the interval that fits your address, your unit, and how your household uses hot water.

San Jose + Santa Clara County

San Mateo County / Peninsula

South Santa Clara County

Want the scale gone without the bucket and pump? Get a quote.

We descale tankless water heaters across San Jose and the surrounding cities, add isolation valves when the unit does not have them, and hand you a dated service record for your warranty file. Tell us your city and your unit and we will send a flat-rate price.

  • Flat-rate pricing quoted before we start — no hourly meter
  • Isolation valves installed on units that were never set up for service
  • Full inspection included: filters, flame rod, venting, gas pressure, outlet temperature
  • Dated maintenance record that protects your manufacturer warranty
Call (408) 470-0191Request my descaling quote

What San Jose customers say

“Had a great experience with the guys at Efficient Water Heaters. Joseph and his employee came out right on time, got to work with no fuss, and a little more than three or four hours later we had a brand new tankless installed in our house. They even swept up the garage cleaner than it was before they got there. Great communication before, during, and afterwards. Would definitely recommend them.”
— Chieze O.
“I asked a lot of questions about tankless. Joseph was quick in responding and the answers were unbiased and helpful. Marco helped us install the water heater. He is efficient, professional, and the job was very well done. Price is fair — I got the best quote comparing with 2 other vendors who have good reviews on Yelp. Highly recommend.”
— Tony C.
“We were in a bind. Had no water and couldn't get ahold of anyone on the weekend. Joseph responded immediately. Scheduled an appointment the next day and gave us a beautiful new tankless hot water heater for the same price as the previous person quoted for a 40-gallon. His work was very nicely done and we are very happy with our new efficient water heater.”
— Celeste G.

Tankless Flushing & Descaling Checklist

Tick the boxes as you work. Use the print button to send this to your printer or save it as a PDF — the printed sheet drops the site navigation and keeps just the checklist.

Date
Unit model / serial
Performed by

Before you start

  • Confirm the unit has hot and cold isolation service valves — no valves means stop and call a pro
  • No gas smell, no water dripping at the unit, no scorching around the vent
  • Gas supply valve closed and power off at the switch or breaker
  • Unit cooled 20–30 minutes before touching any plumbing
  • Bucket, towels, and a clear path to a drain in place

Tools and solution

  • Submersible utility pump
  • Two washing-machine hoses
  • 5-gallon bucket
  • Adjustable wrench
  • 4 gallons of white vinegar or a food-grade descaling solution
  • Replacement inlet filter screen gasket if the old one is worn
  • Clean rinse water

Step-by-step

  • 1. Shut down the unit safely. Turn off the gas supply valve to the unit and cut power at the switch or breaker. Let the unit cool for 20 to 30 minutes before touching any plumbing — the exchanger holds heat well past shutdown.
  • 2. Close the isolation valves and relieve pressure. Close the hot and cold isolation valves so the unit is separated from house plumbing. Open the service port caps slowly with a bucket underneath to relieve pressure and drain the water inside the exchanger.
  • 3. Connect the pump and hoses. Run one hose from the pump in the bucket to the cold service port and a return hose from the hot service port back into the bucket. Fill the bucket with about 4 gallons of white vinegar or descaling solution, then open both service port valves.
  • 4. Circulate the descaling solution. Run the pump for 45 to 60 minutes. In hard-water areas like Morgan Hill or Gilroy, or on a unit that has never been serviced, go the full hour. The solution should darken and carry loose flakes as bonded scale releases.
  • 5. Clean the inlet filter screen. While the solution circulates, remove the cold-water inlet filter screen and rinse the trapped grit out of it. Inspect the gasket, replace it if it is flattened or cracked, then reinstall the screen snugly.
  • 6. Rinse with clean water. Stop the pump, dump the used solution, and refill the bucket with clean water. Circulate for 5 to 10 minutes so no acidic residue stays in the exchanger. Remove the hoses and reinstall the service port caps.
  • 7. Restore service and verify performance. Open the isolation valves, open the gas valve, and restore power. Run a hot tap for two minutes and confirm a steady outlet temperature, full flow, and no error code on the display. Write down the date so your maintenance record stays current.

After the flush

  • Service port caps reinstalled and snug, hoses removed
  • Isolation valves open, gas valve open, power restored
  • Hot tap run for two minutes: steady outlet temperature, full flow
  • No error code on the display after a full hot-water cycle
  • No drips at the service ports or inlet filter housing
  • Date, solution used, and circulation time written in the maintenance log

How often to flush

  • • San Jose, Santa Clara, Sunnyvale, Milpitas: once a year
  • • Cupertino, Saratoga, Los Gatos, Monte Sereno, Los Altos: about every 9 months
  • • Mountain View, Palo Alto, Menlo Park, Redwood City and the mid-Peninsula: every 9–12 months
  • • Morgan Hill, San Martin, Gilroy: every 6–9 months — hardest water we serve
  • • Any home with a recirculation loop or no softener: shorten the interval by about 3 months

Notes

Stop and call a licensed contractor if you smell gas, see a leak, or the unit still shows an error code after a full descaling. Efficient Water Heaters, Inc. — (408) 470-0191, open 24/7, CSLB #1008381.

Free download

Hard Water Tankless Flushing Checklist (PDF)

A printable, two-page checklist of everything on this page — the pre-flush safety checks, the tools and solution you need, the seven flushing steps in order, what to verify afterward, and how often to flush based on where you live in the South Bay. Enter your email and we'll send it over.

  • Pre-flush safety checks and the red flags that mean stop
  • Complete tool and descaling-solution list
  • The 7-step flush sequence with timing for hard-water homes
  • Post-flush verification and maintenance log prompts
  • Flushing intervals by city, from San Jose to Gilroy

We'll send the PDF and occasional Navien maintenance reminders. No spam, and you can unsubscribe any time.

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Send a photo of your water heater's data plate for a faster estimate

The data plate is the metal or sticker label on the side or front of the unit. Snap a clear photo of it, attach it to the form below, and we can price your descaling before we ever get on the phone.

  • The plate shows the model and serial number, so we know the exact heat exchanger and parts
  • The serial tells us the unit's age, which predicts how heavily scaled it likely is
  • A second photo of the pipes below the unit shows us whether isolation valves are already installed
  • Use the "Photo of your unit or data plate" field in the form — it takes multiple images

Send a photo of your data plate for a faster estimate.

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Efficient Water Heaters, Inc. · Joseph J. Castro, Owner · CSLB #1008381 · (408) 470-0191 · Navien tankless service in San Jose

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