Symptom guide
No hot water: find the right diagnostic path
Start with heater type and whether the water is completely cold, briefly hot, or only lukewarm. Then choose the matching brand or system guide.
Safety first: Leave a breaker off if it trips again. If you smell gas, leave the building and call the gas utility from outside.
Start here
Identify the unit before following a procedure
Photograph the rating plate, control or display, and the exact symptom. Model generations can use different controls and code meanings even when the brand name is the same.
- Choose the heater typeGas tank, electric tank, tankless, heat pump, indirect, or RV.
- Record the exact clueCode, flash count, leak location, sound, or timing.
- Use the closest guideConfirm every model-specific step against the label or manual.
Gas
1 guideElectric
10 guidesAO Smith Hybrid Problems: Codes
A. O. Smith Voltex hybrid not heating? Common causes are a dirty filter, vacation mode, an element or ECO fault, a compressor code, or a leak.
BoschBosch Powerstar Tankless Troubleshooting
A Bosch Powerstar tankless not heating may have a dead 240 V leg, low flow, a stuck flow sensor, a tripped thermal cutout, or reversed lines.
Bradford WhiteBradford White Electric Not Heating Up
A Bradford White electric not heating usually has a tripped breaker, a popped ECO, a failed upper element, or a bad thermostat. How to narrow it.
ElectricElectric Tankless Goes Cold Mid-Shower
An electric tankless shutdown can involve power, flow, or protective controls. Record the fault and learn when to arrange professional service.
ElectricEnergy Smart Water Heater Troubleshooting
Energy Smart electric tank not heating? Causes include power loss, E01 dry fire, E02 high limit, element codes, or a module fault.
LochinvarLochinvar Electric Water Heater Troubleshooting
A Lochinvar electric tank not heating usually has a tripped breaker, a popped ECO, a failed element, or a thermostat fault. How to narrow it.
A. O. SmithNew AO Smith Electric Not Heating
A new AO Smith electric that is ice-cold is fill, 240 V, ECO, or an install miss. Do not dry-fire it.
ElectricNew Element, Still No Hot Water
Replaced an element and still no hot water? The other element, the thermostat or ECO, a breaker, the wiring, or a dry fire may be to blame.
RheemRheem Heat Pump Water Heater Problems
A Rheem hybrid not heating may have a dirty filter, vacation mode, an EcoNet code, a tripped ECO, a failed element, or a compressor lockout.
SeiscoSeisco Tankless Water Heater Troubleshooting
A Seisco tankless not heating usually has a missing 240 V leg, air in the chamber, a high-limit trip (122), or a leak detect code (126).
Tankless
12 guidesAO Smith Tankless With No Hot Water
An A. O. Smith tankless with no hot water usually has no 120 V, no flow signal, a lockout code, or no gas. Read the display before resetting.
AtmorAtmor Tankless Water Heater Troubleshooting
An Atmor tankless passing cold water usually has no 240 V, too little flow, a clogged screen, reversed lines, or too little kW for the fixture.
NavienNavien Goes Cold After a Few Minutes
A Navien that goes cold after a few minutes usually has low flow, a recirculation cold slug, flame loss (E012), or scale overheating (E016).
NavienNavien Water Heater Not Getting Hot
A Navien that never reaches its set temperature may be undersized, scaled, limited by a mixing valve, crossed over, or short on gas supply.
NoritzNoritz Tankless Not Hot Enough
A Noritz running lukewarm may be undersized, scaled, limited by a mixing valve, crossed over, short on gas, or simply set too low.
NoritzNoritz Tankless With No Hot Water
A Noritz with no hot water usually has no 120 V, no flow signal, a lockout code, or a gas or ignition fault. Read the display first.
RinnaiRinnai Goes Cold After a Few Minutes
A Rinnai that goes cold after a few minutes usually has flow dropping below minimum, flame loss (code 12), or scale overheating (code 16).
RinnaiRinnai Not Getting Hot Enough
Lukewarm Rinnai water is undersize, scale, a mixing valve, or gas — not a hidden turbo. Measure inlet temp and GPM.
RinnaiRinnai Tankless With No Hot Water
A Rinnai with no hot water usually has no 120 V, no flow signal, a lockout code, or a gas or ignition fault. Read the display first.
TakagiTakagi Tankless Problems: Codes & Fixes
Takagi tankless not heating? Most lockouts are air or exhaust faults (10), ignition or flame loss (11/12), or overheating from scale (14/16).
TakagiTakagi Tankless Water Heater Not Heating
A Takagi tankless that will not heat needs flow, power, gas, ignition, or scale checks. Photograph the code.
TanklessTankless: No Hot Water at the Kitchen Sink
Kitchen cold while the shower is hot is an aerator, crossover, or min-flow — not a new unit. Diagnose it.
RV
5 guidesGirard Tankless Troubleshooting: Codes & Lockouts
Girard RV tankless not heating? Most cases are an E1/E2 ignition lockout, low 12 V, an ECO trip, a probe fault, or freeze mode. What each means.
RVRV Water Heater Not Getting Hot Enough
Lukewarm RV hot water is usually a half-open bypass valve, one heat source not working, or a mixing valve. How to find the cause.
SuburbanSuburban SW10DE Troubleshooting Guide
Suburban SW10DE not heating on gas or electric? Check the ECO, bypass valves, shore power, DSI board, and igniter, starting with a full tank.
SuburbanSuburban SW6DE Troubleshooting Guide
Suburban SW6DE not heating on gas, electric, or both? Check the ECO, bypass valves, shore power, and DSI ignition, and never heat an empty tank.
SuburbanSuburban Tankless Troubleshooting
A Suburban Nautilus tankless not heating usually has an E1/E2 ignition lockout, low flow, low 12 V, an overheat code, or freeze damage.
Troubleshooting
15 guidesApartment Water Heater Not Hot Enough
Lukewarm apartment water is a mixing valve, crossover, dead element, or building recirc — not a bigger tank.
AristonAriston Water Heater With No Hot Water
A cold Ariston usually has no power, a tripped ECO, a failed element, or a thermostat fault. Checks for Andris, Velis, Pro1, and tankless models.
Bradford WhiteBradford White Not Hot Enough
Lukewarm Bradford White water is a dip tube, lower element, mixing valve, or setpoint — not “buy a bigger tank.” Diagnose it in order.
TroubleshootingBrand New Water Heater Has No Hot Water
A brand-new tank with no hot water is usually an install issue: closed valves, an unfilled tank, power or gas off, or a misplaced dip tube.
TroubleshootingBrand New Water Heater Only Runs Warm
A new water heater that only runs lukewarm is usually a mixing valve, misplaced dip tube, unwired element, or vacation setting. How to check.
TroubleshootingCan You Use Water If the Water Heater Is Leaking?
You can keep cold water on if you close the heater's cold inlet, but running hot water through a leaking tank empties it. What to do first.
TroubleshootingCold Water Inlet Leaking on the Heater
A leak at the cold water inlet is usually a dielectric nipple, heat trap, connector, or Hydrojet adapter, not the tank. How to find it.
TroubleshootingHow to Shut Off an Apartment Water Heater
Leaking apartment heater? Shut off cold water, then gas or the 240V breaker only if safely accessible. Notify the landlord immediately.
TroubleshootingNo Hot Water After Flushing the Tank
Cold showers after a flush are a dry-fire, tripped ECO, out pilot, or a breaker. Do not reset empty.
RheemRheem Water Heater Not Heating
A Rheem not heating needs different checks for gas and electric: breaker, ECO, elements, and thermostat, or pilot, FVIR, and gas control.
RichmondRichmond Water Heater Has No Hot Water
A Richmond with no hot water needs a different check for gas and electric: breaker, ECO, element, or thermostat versus pilot, FVIR, or control.
TroubleshootingSolar Water Heater No Hot Water in the Morning
A solar water heater cold in the morning may have a freeze dump, a pump running overnight, a stuck mixing valve, or a failed backup heater.
StateState Select Water Heater No Hot Water
A State Select with no hot water needs different checks for electric and gas: breaker, ECO, and element versus igniter, FVIR, and gas control.
TroubleshootingWater Heater Beeping and No Hot Water
Beeping with no hot water usually means a tankless or hybrid lockout, a dry-fire alarm, a power-vent fault, or a leak sensor that cut the heat.
Weil-McLainWeil-McLain Indirect Water Heater Problems
A Weil-McLain AquaPlus indirect with no hot water usually has a sensor, pump, zone valve, priority, or air problem. How to narrow it down.