Tankless water heater repair in San Jose, any make
Tankless repairs are the core of what we do, and most error codes point to a fixable part rather than a dead unit.
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- Phelan Ave San Jose office
- Tank, tankless, heat pump
Perfect Tankless Plumbing, San Jose, CA
Tankless water heater repair in San Jose starts with the error code and the unit's history; the usual causes are scale on the heat exchanger, a clogged inlet filter, a failed igniter or flame sensor, a flow sensor fault or a venting problem, and most are repaired in one visit with the unit descaled while it is open.
Updated September 2026
Water Heaters
Why tankless units stop working
A tankless heater is a set of sensors, a burner, a fan and a heat exchanger, each with its own failure pattern. The error code narrows it down; testing confirms it. Replacing parts by guesswork gets expensive quickly.
In San Jose, scale is often behind the fault even when the code names another part, so a repair visit usually includes descaling while the unit is open.
Warning signs
Signs your tankless unit needs repair
- Error code on the displayThe unit has diagnosed a fault.
- Water goes cold mid-showerFlow, gas or scale.
- Unit does not fire on small drawsFlow sensor or filter.
- Temperature swingsScale or a mixing valve.
- Loud fan or whistlingVenting or fan issue.
- Water at the baseCondensate or a fitting leak.
Error code diagnosis
Every brand has its own error codes, and many point to a category rather than a single part: ignition failure, flame loss, overheating, flow problems or venting. We read the code and the unit's error history, then test the likely components with a meter and the manufacturer's diagnostic steps. Knowing whether an ignition fault is the igniter, the gas supply or a blocked vent saves you paying for parts that were not the problem, which is the most common complaint we hear from owners who have already had a tankless unit serviced elsewhere.
Ignition failure
When a tankless unit tries to fire and gives up, the cause is usually the igniter, the flame sensor, low gas pressure or a blocked air intake. We check gas pressure at the unit while it runs, inspect and clean the flame sensor, test the igniter and look at the intake screen and venting. Undersized gas lines cause ignition faults under high demand, which is common when a unit was installed without upsizing the line from the old tank heater, and no replacement part will fix that.
Cold water sandwich
A burst of cold water between two hot ones happens when the unit shuts down briefly between uses and has to relight. It is a characteristic of tankless heating rather than a fault, but it can be reduced with a small buffer tank, a recirculation setup or adjusted settings. We check that the unit is not also short-cycling because of a low flow sensor setting or scale, which makes the effect much worse than it should be and is easy to correct once it is found.
Flow sensor and valve faults
A tankless unit fires only when its flow sensor sees water moving above a minimum rate. A scaled or failed sensor means the unit ignores small draws or fires erratically. Mixing valves and bypass valves inside some models also stick with hard water. We clean or replace the sensor, check the inlet filter and the valves, and confirm the unit fires at a low flow and holds temperature at a high one before closing it up and handing it back to you with the error history cleared.
How the job runs
How a tankless repair runs
- 1
Read the code
And the error history.
- 2
Check gas and venting
Pressure and airflow.
- 3
Test components
Sensors, igniter and fan.
- 4
Replace or clean
The confirmed part.
- 5
Descale if needed
While the unit is open.
- 6
Test
Low and high flow, temperature hold.
Local context
Hard water behind many San Jose tankless faults
San Jose Water Company describes the white film homeowners see on showerheads and glass as residue of hardness, left behind when water heats or evaporates. Inside a tankless unit the same minerals settle on the heat exchanger and flow sensor, where the result is not a stain but an error code. That is why so many tankless repair calls here end with descaling as well as the part, and why we fit service valves if the unit lacks them.
DIY or call
Tankless checks you can do
| Task | Reasonable to DIY | Call a plumber |
|---|---|---|
| Noting the error code | Yes | To diagnose it |
| Cleaning the inlet filter | Yes, valves closed | If flow stays low |
| Checking the gas valve is open | Yes | If it is open and still faults |
| Power cycling the unit | Once | If the code returns |
| Replacing sensors | No | Always |
| Adjusting gas pressure | No | Always |
Cost factors
What tankless repair costs depend on
We do not publish a local tankless repair price; the part and any descaling set the scope.
- Failed part. sensor, igniter, fan or board
- Brand and model. parts availability varies
- Descaling. often done on the same visit
- Gas supply issues. may need line upsizing
- Venting problems. blocked or damaged vents
- Unit age. older units may not be worth major parts
FAQ
Tankless Water Heater Repair questions from San Jose homeowners
We work on the common brands and source parts by model.
Often yes, if the heat exchanger is sound. We tell you if it isn't.
Usually scale, a flow sensor issue or an undersized gas supply.
Yes, when scale is part of the problem, which it often is here.
It can be reduced with settings, a buffer tank or recirculation.
Same family
Related work in water heaters
Boiler Repair and Replacement
No heat or low pressure, Relief valve and expansion tank faults.
How we handle boiler repair and replacementNoritz Tankless Water Heater Repair
No ignition and flame failure, Scale and flow problems.
Noritz Tankless Water Heater RepairTankless Descaling and Flush
Isolation valve retrofit, Inlet filter cleaning.
Isolation valve retrofit and related workHeat Pump Water Heater Installation
Hybrid 240V units, Condensate and clearance planning.
Read about heat pump water heater installationRecirculation Pump Installation
Dedicated return line, Under-sink crossover.
Recirculation Pump Installation in San Jose
From our guides: Tankless goes cold, explained, Read the guide on how often to flush tankless, Rinnai error codes, explained.
One number, any hour
Get your tankless unit running again
Call any hour and tell us the error code. We will bring the likely parts.
