Tankless Water Heater Repair in Castle Rock & Douglas County, CO

Tankless water heaters are efficient, long-lasting, and reliable — but when they have a problem, diagnosing and repairing them requires a technician who actually understands the technology. PS Cool Heat provides expert tankless water heater repair throughout Castle Rock, Parker, Highlands Ranch, Lone Tree, Littleton, Greenwood Village, Ken Caryl, and the greater Douglas County area.

We service all major tankless brands, interpret error codes accurately, descale heat exchangers, replace sensors and components, and address the root cause of the problem — not just the symptom. If your tankless water heater is displaying an error, producing cold water, making unusual sounds, or just not performing the way it should, call PS Cool Heat.

Call us at 720-613-2210 to schedule tankless water heater repair.

Why Is My Tankless Water Heater Not Working?

Tankless water heaters have specific components and failure modes that differ from traditional tank units. These are the most common issues we diagnose and repair:

Error Codes on the Display

Modern tankless water heaters are equipped with self-diagnostic systems that display error codes when something is wrong. These codes are brand-specific — a code on a Rinnai unit means something different than the same number on a Navien or Noritz. PS Cool Heat technicians know how to interpret error codes accurately across all major brands and use them as a starting point to diagnose the actual failure rather than just resetting the unit and hoping for the best.

No Hot Water

If your tankless unit is running but not producing hot water, the problem could be an ignition failure (gas units), a failed flow sensor, a tripped high-limit switch, or a failed heating element (electric units). Each has a different diagnosis and repair pathway.

Water Is Warm but Not Hot Enough

Insufficient heating is often related to a faulty temperature sensor or thermistor, a partially blocked heat exchanger, a gas pressure issue, or — very commonly in Douglas County — scale buildup inside the heat exchanger reducing its ability to transfer heat efficiently.

Unit Won’t Ignite (Gas Models)

Ignition failures in gas tankless units can be caused by a faulty igniter, a bad flame sensor, inadequate gas pressure, a problem with the gas valve, or venting issues preventing proper combustion airflow. This is one of the more complex diagnostics on a tankless unit, and it requires someone who understands the ignition sequence for the specific brand.

Cold Water Sandwich

The “cold water sandwich” is a phenomenon specific to tankless water heaters where a brief burst of cold water appears in the middle of a hot water use — most noticeably when you turn the shower off and then back on. It’s caused by residual cold water sitting in the pipes between uses. In some cases, it’s normal and expected; in others, it’s a symptom of a unit that’s slow to ignite or has a flow sensor problem.

Fluctuating Water Temperature

If your water temperature fluctuates significantly during use, the cause might be a failing thermistor, a flow sensor that’s not reading accurately, or a gas pressure fluctuation. In households with multiple simultaneous demands, it can also indicate an undersized unit.

Scale Buildup in the Heat Exchanger

This is the single most common cause of performance degradation and service calls for tankless water heaters in Castle Rock and Douglas County. The area’s hard water (18–22 grains per gallon) causes rapid calcium and magnesium scale buildup inside the heat exchanger — the heart of the unit. Scale reduces heat transfer efficiency, triggers error codes, causes the unit to overheat and shut down, and eventually leads to permanent heat exchanger damage if not addressed. Regular descaling is not optional in this area — it’s essential maintenance.

Venting Problems (Gas Models)

Blocked, improperly installed, or damaged venting on a gas tankless unit creates combustion air supply issues and exhaust backpressure that can prevent the unit from operating, trigger error codes, and in extreme cases pose a carbon monoxide risk. PS Cool Heat inspects and repairs venting systems on all gas tankless installations we service.

Water Leaks

Leaks from a tankless unit can come from the pressure relief valve, inlet or outlet connections, internal heat exchanger corrosion, or a failed component seal. The source and severity vary, but any leak from a water heater should be assessed promptly.

Unit Keeps Shutting Off

Repeated shutdowns are usually the unit’s safety systems protecting itself from a condition it can’t operate in — overheating from scale buildup, an exhaust blockage, inadequate gas supply, or a faulty sensor reporting a false condition. A unit that keeps shutting itself off needs a diagnosis, not just a restart.

What PS Cool Heat Repairs on Tankless Units

• Error code diagnosis and interpretation — all major brands
• Heat exchanger descaling and chemical flush — critical maintenance in Castle Rock
• Flow sensor replacement
• Thermistor and temperature sensor replacement
• Igniter replacement (gas)
• Flame sensor / flame rod cleaning and replacement (gas)
• Gas valve repair and replacement (gas)
• Burner assembly inspection, cleaning, and replacement (gas)
• Venting system inspection and repair (gas)
• High-limit switch reset and replacement
• Pressure relief valve replacement
• Inlet and outlet connection repair and re-sealing
• Control board and circuit board diagnosis and replacement
• Water filter and inlet screen cleaning
• Thermal fuse replacement (electric models)
• Heating element replacement (electric models)

Why Douglas County’s Hard Water Is Hard on Tankless Water Heaters

Castle Rock, Parker, Highlands Ranch, and the surrounding Douglas County area draw water from the Denver Basin aquifer system — one of the hardest groundwater sources along the Colorado Front Range. Water hardness in this area typically registers between 18 and 22 grains per gallon (gpg), which is classified as very hard.

For a tankless water heater, this creates a specific challenge. Every time the heat exchanger fires to heat water, dissolved calcium and magnesium minerals are forced out of solution and deposit on the metal surfaces of the heat exchanger. Unlike a storage tank where sediment falls to the bottom, scale in a tankless unit coats the heat transfer surfaces directly — exactly where efficient heating depends on maximum contact between hot metal and flowing water.

What happens as scale accumulates:

• The heat exchanger has to work harder and run longer to reach set temperature — energy efficiency drops
• The unit triggers overtemperature errors because it’s running hotter than it should
• Performance becomes inconsistent — water temperature fluctuates
• Specific error codes appear (Rinnai Code 14, Navien Code E012, and others) indicating overheating
• The heat exchanger can be permanently damaged, requiring expensive replacement

Annual Descaling Keeps Your Unit Running Properly

PS Cool Heat performs professional heat exchanger descaling using a food-safe, manufacturer-approved descaling solution circulated through the unit with a dedicated flush kit. This process

dissolves accumulated calcium and magnesium scale, restoring heat transfer efficiency and clearing any blockages in the flow path.

In the Castle Rock and Douglas County area, we recommend this service annually. Homes with particularly hard water or high hot water usage may benefit from twice-yearly service.

The Long-Term Solution: Water Softener Installation

Descaling treats the problem after it occurs. A whole-home water softener prevents it from happening in the first place by removing hardness minerals from the water supply before they reach your tankless unit.

For homeowners who want to protect their tankless investment and minimize ongoing maintenance, pairing a tankless water heater with a whole-home water softener is the best approach available. Ask PS Cool Heat about water softener installation in Castle Rock and Douglas County — we handle both services.

Common Error Codes by Brand

Tankless water heater error codes are self-diagnostic messages generated by the unit’s control board to indicate a specific problem. While brand-specific codes vary, here are common categories PS Cool Heat addresses:

Ignition Failure Codes

Indicate the unit attempted to ignite and failed — could be the igniter, flame sensor, gas valve, or gas supply. On Rinnai units, this often appears as Code 11. On Navien, Code E003 or E004. Our technicians diagnose the specific cause, not just the code.

Overheating / High Temperature Codes

The unit’s heat exchanger or outgoing water temperature exceeded the safety threshold. In Castle Rock and Douglas County, this is very frequently caused by scale buildup forcing the heat exchanger to overheat. Annual descaling prevents this.

Flow Sensor / No Flow Codes

Indicates the unit isn’t detecting sufficient water flow to activate. Could be a flow sensor failure, low water pressure, a partially closed valve, or a clogged inlet filter screen.

Exhaust / Venting Codes

Gas units will generate errors if exhaust backpressure is detected or if the vent is blocked. These are important to address promptly — improper venting on a gas appliance is a safety concern.

Whatever code your unit is displaying, PS Cool Heat will diagnose the root cause and provide a clear repair recommendation. Call 720-613-2210.

Tankless Water Heater Brands PS Cool Heat Repairs

Our technicians are trained on all major residential tankless water heater brands:

• Rinnai — one of the most widely installed brands in the Denver area; we service all current and legacy Rinnai models
• Navien — NPE series condensing tankless units; we diagnose and repair all Navien error codes
• Noritz — known for reliable gas tankless systems; full repair service available
• Rheem — both gas and electric tankless models serviced
• A.O. Smith — Voltex and tankless gas series
• Bradford White — commercial and residential tankless models
• Bosch — Greentherm series and point-of-use models
• EcoSmart — electric tankless models
• Takagi — commercial and residential gas tankless
• State Water Heaters — ProLine series tankless

Don’t see your brand? Call us at 720-613-2210 — we likely service it.

When Should I Repair My Tankless Water Heater vs. Replace It?

Tankless water heaters are built to last 20+ years — far longer than tank units — so repair is usually the right call unless the unit is very old or has suffered catastrophic damage. Here’s how we think about it:

Repair is typically the right call when:

• The unit is under 15 years old
• The failure is a specific component — sensor, valve, igniter, flow sensor
• Scale buildup is the issue (descaling restores performance)
• The heat exchanger is intact and functional

Replacement may make more sense when:

• The heat exchanger is cracked or permanently scaled beyond recovery
• The control board has failed on an older unit where parts are no longer available
• The unit is 18–20+ years old and on its second or third major failure
• The unit was undersized for the home’s demand from the beginning, causing chronic problems

PS Cool Heat will give you a straight answer. We don’t recommend replacement if repair is the right call for you.

Serving Douglas County and the South Denver Metro

• Castle Rock
• Parker
• Highlands Ranch
• Lone Tree
• Littleton
• Greenwood Village
• Ken Caryl
• Sedalia
• Franktown
• Douglas County unincorporated communities