QuietSide Tankless and Combi Heater Problems
On this page (7 sections)
The Short Answer: Most QuietSide units in homes are QVM-series condensing gas combi units that heat both the house and the tap water. When the hot water stops, the cause is usually power, gas supply, a blocked vent or condensate drain, a clogged domestic water strainer, or the diverter valve that switches between heating and hot water. Write down any error code and read it from your own manual.
Why a combi unit fails differently
A QuietSide combi has one burner that serves two jobs. A diverter (three-way) valve sends the heat to your radiators or floor loops, or to a heat exchanger for tap water. That means you can have:
- No heat and no hot water: the burner is not running. Think power, gas, venting, or a lockout.
- Heat but no hot water: the burner works, but the domestic side is not getting its share. Think diverter valve, the domestic flow sensor, or a clogged strainer.
- Hot water but no heat: a heating-loop problem such as low loop pressure or a pump.
Reading the error code
QuietSide units report faults as a number on the display or room controller. The code list differs by model and generation, and it is not the same as Rinnai, Navien, or Noritz code lists. Use the owner’s manual for your exact model (the model number is on the rating plate inside the lower cover or on the side). Some faults shut the unit down without lighting the check lamp; the manual explains how to display the code. If you no longer have the manual, a heating contractor familiar with Korean-built combi equipment can usually read it.
Common patterns
| What you notice | Likely cause | Urgency |
|---|---|---|
| Display dark | No 120-volt power, or a failed control board | Low; check power first |
| Fan runs, then a code and no flame | Gas supply, ignition, or vent and air intake | Moderate; one reset only |
| Radiators warm, taps cold | Diverter valve, domestic flow sensor, or clogged strainer | Moderate |
| Heating stops, low-pressure or low-water code | Heating loop pressure dropped, possibly a leak | Moderate |
| Water under the unit | Condensate drain, relief valve, or an internal leak | Moderate; check where it comes from |
| Exhaust smell indoors | Vent leak or combustion problem | High; shut it off and leave |
What you can check safely
- Record the error code and when it appears.
- Confirm the unit has power and that the gas supply valve is open; check that other gas appliances work.
- Look at the outdoor vent and intake terminations for snow, ice, leaves, or nests.
- Check that the condensate drain line is connected and not kinked or frozen.
- Read the heating-system pressure gauge if your system has one, and compare it with the range in your manual.
- Reset once after fixing an obvious cause. Repeated resets on an ignition fault can leave unburned gas in the combustion chamber.
What the technician will check
A technician will interpret the code against the service literature, test ignition and flame sensing, check gas pressure with the burner running, and inspect the fan and air pressure switch. For hot-water-only complaints they check the domestic strainer, the flow sensor, and the diverter valve motor and cartridge. They also look for scale in the domestic heat exchanger, a common problem with hard water.
Repair or replace
QuietSide equipment has limited parts support in North America, so repair depends on whether the needed part can still be found. Strainer cleaning, sensors, and some fans or diverter parts are often obtainable. A cracked heat exchanger, a failed board with no replacement, or repeated lockouts on an older unit usually point toward replacement. Ask the technician to confirm part availability before authorizing diagnostic work.
Related: tankless water heater exhaust smells like gas and tankless water heater not working after rain.
Frequently Asked Questions
Q: Can I use a Rinnai or Navien code chart for my QuietSide? A: No. Code numbers are assigned by each manufacturer, and the same number can mean different things. Use the manual for your QuietSide model.
Q: Why do my radiators work but the taps stay cold? A: The burner is working, so the domestic side is not getting heat. The usual suspects are the diverter valve, the domestic flow sensor, or a clogged strainer on the cold inlet. These are service items for a technician.
Q: Is it worth repairing an older QuietSide? A: It depends on parts. Get a firm diagnosis and confirmation that the part is available before paying for repairs on a unit that is more than about 15 years old.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
Editorial standards and corrections · Prepare a useful service request