Noritz Tankless Not Hot Enough: Lukewarm Water
On this page (7 sections)
The Short Answer: If a Noritz fires but the water is only lukewarm, check the temperature setting and maximum-temperature setting first, then whether you’re asking for more flow than it can heat. Noritz’s guide also points to a clogged inlet filter and to scale from untreated hard water, which it says can be removed by flushing. A failed mixing or shower valve can make water lukewarm too.
Where to look first
| Clue | Likely cause |
|---|---|
| Lukewarm everywhere, even with one fixture | Setting, maximum temperature limit, filter, scale, or gas supply |
| Fine with one shower, lukewarm with two or more | Flow beyond the heater’s capacity for the temperature rise |
| Worse in winter | Colder incoming water needs more heating |
| Gradually worse over months or years in a hard-water area | Scale on the heat exchanger |
| Lukewarm at one fixture only | That fixture’s mixing valve or anti-scald limit |
| Cold tap runs warm somewhere | Crossover between hot and cold lines |
If water goes hot then cold during use, see tankless goes hot to cold. If it never heats at all, see Noritz no hot water.
Settings
Noritz’s guide asks, for a temperature that won’t rise, whether the maximum temperature setting is appropriate. Check both the set temperature on the remote and any maximum limit the installer configured.
Noritz suggests a setting of about 115°F to 120°F (48°C to 50°C) for fluctuating temperatures or reduced hot water. At that setting, you use more hot water and less cold at the fixture, which keeps flow through the heater above the 0.5-gallon-per-minute minimum.
Capacity
Every tankless heater has a limit. For the NRC1111, Noritz gives a maximum of 8.4 gallons per minute at a 45°F rise. A larger rise means less flow. On a cold winter day you may need a 70°F rise, and the heater can deliver much less hot water at that rise than in summer. If two showers and a dishwasher run together, you may be past what it can heat. Spreading out use, or a second heater, are the realistic fixes.
Filter and scale
- Inlet filter. Noritz links a clogged water drain valve filter to temperature problems and gives owner cleaning steps: close the water supply, open hot fixtures, drain, remove and brush the filter, reinstall, and check for leaks.
- Scale. The guide says untreated hard water causes scale buildup that decreases the maximum amount of hot water, and that flushing removes it (see how to flush a tankless water heater). Noritz’s water quality table gives 200 mg/L (about 12 grains per gallon) as its suggested maximum hardness. Above that, treat the water to keep full warranty coverage. Flushing needs isolation valves, which Noritz sells as an accessory, and is normally done by a plumber.
What you can check safely
- Check the set temperature and maximum limit on the remote.
- Measure the water at the nearest tap with a kitchen thermometer.
- Test with one fixture at a time.
- Clean the inlet filter if you’re comfortable following the guide.
- Note whether it’s worse in winter or with other gas appliances running.
What the technician will check
A technician will compare inlet and outlet temperatures and flow, and flush the heat exchanger if scale is present. They measure gas pressure at full fire with other appliances running, and check mixing valves and plumbing for crossovers. If the heater is undersized for your peak use, they can explain the options.
Frequently Asked Questions
Q: Should I raise the Noritz to its highest setting? A: Not as a first step. A higher setting won’t add capacity, and it raises the scald risk. Check the filter, scale and flow first, and use a mixing valve if higher storage temperatures are needed.
Q: How often should a Noritz be flushed? A: It depends on water hardness and use. In hard-water areas, yearly is common. If your water exceeds Noritz’s hardness target, ask a plumber about treatment as well.
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.
- Noritz NRC1111 owner's guide (SBA8723) (opens in a new tab)Noritz NRC1111-DV and NRC1111-OD: temperature troubleshooting, 0.5 GPM minimum flow, filter cleaning, water quality targets.
- Noritz: product support and technical literature (opens in a new tab)Find the specific model’s owner guide and code definitions.
- Stiebel Eltron: Tempra engineering specifications (opens in a new tab)Flow, temperature-rise and power relationship; product ratings apply only to the named Tempra models.
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