(And What I Check First on Every Job)

Tankless water heaters are amazing when they’re working right.
Endless hot water. High efficiency. Low profile.

But when they stop working?

You go from “smart plumbing system” to “why is the shower freezing” real fast.

I’ve worked on dozens of these units here in Sacramento, and I can tell you:
The same 5 or 6 problems show up again and again.
Here’s what usually goes wrong — and what I check first when I’m called out to fix one.

1. Mineral Buildup (The #1 Killer in Sacramento)

If your tankless water heater suddenly shuts down, gives error codes, or the water just won’t stay hot — my first guess?

Hard water scale.

Sacramento has hard water. It leaves calcium deposits in the heat exchanger, sensors, and pipes. Over time, that blocks the flow, confuses the sensors, and forces the unit to overheat.

What I check first:

• Service history (has it ever been flushed?)
• Flow rate drop
• Burner pattern
• Internal filters and screen

Fix: A full flush with descaler, and sometimes a filter replacement.
Skipping flushing? That’s how heaters die early.

2. Ignition or Flame Failure

If you’ve got a gas-powered tankless unit, and it just won’t fire — it might not be getting a spark or clean ignition.

Causes I often see:

• Dirty or corroded ignitor
• Blocked gas line
• Poor venting or backdraft
• Low gas pressure
• Faulty flame sensor

What I check:

• Vent pipes for blockages
• Ignitor cleanliness
• Sensor reading during startup
• Error codes (they help a lot)

Fix: Sometimes it’s just a deep clean. Sometimes, a part swap.

3. Air Supply or Exhaust Blockage

Tankless heaters are picky about airflow.
If the intake is blocked (by lint, debris, or even spiderwebs), the unit will shut down to protect itself.

What I check:

• Intake vents (indoor and outdoor units)
• Exhaust flow
• Birds’ nests, insulation, leaves — I’ve seen it all
• Condensation drains (tankless units can back up if clogged)

Fix: Clear the vents. Replace or clean air filters. Confirm vent pipe angles.

4. Error Codes or Reset Loops

Modern tankless systems are smart.
If they think something’s wrong, they’ll shut down and flash a code.

Common codes I’ve seen:

• E1, E2: ignition or flame sensor issues
• E3: flow restriction
• E5: temperature sensor failure
• E9: overheating

What I check:

• Code history (on the display or log)
• Flow rate sensors
• Water pressure in/out
• Temperature sensor readings

Fix: Depends — could be a wire, a sensor, or just a stuck filter.

5. Water Supply Issues

Sometimes the problem isn’t the unit — it’s the incoming water.

Low pressure = no activation
Dirty water = clogged filter
Incorrect valve settings = partial flow

What I check:

• Shut-off valves fully open?
• Cold water line pressure?
• Are any isolation valves closed or installed wrong?

Fix: Quick adjustment, valve reset, or filter clean.

What I Always Ask the Homeowner

When I show up on a tankless call, I always ask:

• Has it ever been flushed? When?
• Did it work perfectly… and then suddenly stop?
• Any noises, smells, blinking lights?
• Was anything else done in the house recently? (new gas line, remodel, etc.)

These clues save a lot of time — and money.

What We Do at Golden Valley Plumbing

We don’t just reset your unit and walk away.
We troubleshoot it the right way — starting with what fails most often, and working down.

Our team:

• Flushes with pro-grade descalers
• Diagnoses sensor and ignition failures
• Replaces what’s needed — not what’s convenient
• Walks you through the fix so you understand it
• Helps prevent it from happening again

If your tankless unit isn’t working — call Golden Valley Plumbing.
We’ll figure out what went wrong — and get your hot water back fast.

Final Thought

Tankless water heaters are efficient — but they’re not magic.
They need air, flow, fuel, and care.

When something goes wrong, don’t panic.
Just get someone who knows what to look for — and how to fix it the right way.