Lochinvar diagnostics differ from standard tank troubleshooting because the products span combi boilers, indirect tanks (no burner), heat pumps, and commercial. Different platforms, different first checks.
NOBLE / KNIGHT Combi — No DHW
- Read the error code on the control display. See Lochinvar error codes
- DHW priority: verify the unit is in DHW mode when a hot tap opens. The flame icon should activate within 5-10 seconds
- Flow switch: minimum activation flow is ~0.6 GPM. Low-flow aerators or partly-closed shutoffs can drop below threshold — open the tap fully
- DHW thermistor (E33): if the sensor reads open or shorted, DHW won\'t activate
- Plate heat exchanger scale: if DHW lukewarm or flow drops over months, scale buildup in the plate exchanger is the cause — descale required. See plate exchanger page
- Diverter valve stuck in heating position — actuator fault; replace
NOBLE / KNIGHT Combi — No heat (but DHW works)
- System pressure: read the gauge — should be 12-15 PSI cold. Below 10 PSI triggers E02 lockout. Re-pressurize via fill valve
- Air in system: bleed all radiator/baseboard high points; bleed the auto-air-vent at the boiler
- Circulator running: listen for hum at the system pump. If silent, electrical or seized impeller
- Thermostat call: verify 24V signal arriving at boiler call-for-heat terminals
- Outdoor reset (if equipped): may be holding off heat in mild outdoor conditions — normal
SQUIRE Indirect — Cold tank water
The SQUIRE has no burner of its own. If the tank is cold, the issue is upstream:
- Boiler running for DHW priority: the tank aquastat should signal the boiler when the tank drops below setpoint. If boiler isn\'t firing on DHW call, the priority wiring or aquastat is at fault
- Tank aquastat setpoint: set to 140°F at the tank; the tank coil heats the stored water from there
- Boiler temperature setpoint: on a mod-con paired with SQUIRE, boiler often runs 180°F on DHW call to maximize heat transfer through the coil. Below 160°F, recovery drops significantly
- DHW priority not enabled: some setups need DHW priority enabled in the boiler controls — see commissioning checklist
- Circulator pump on boiler-to-tank loop: verify the indirect loop circulator is running on DHW call
- Coil scaled: if recovery degraded over years, scale on the boiler-side of the coil reduces heat transfer; pull and inspect
AWHP Heat Pump
- Mode setting: "Heat Pump Only" in cold ambient = inadequate output. Switch to "Hybrid"
- Breaker: 30A double-pole, repeated trips = compressor or wiring
- Air filter: clogged filter shuts down heat pump mode — vacuum monthly
- Condensate drain: blocked → safety shutoff. Clear the trap
- Ambient temp: below 40°F, unit reverts to resistance backup (high cost, slow recovery)
EnergyRite / ARMOR Commercial
- EnergyRite atmospheric: standard chimney draft diagnostics. Check vent, combustion air supply, gas pressure
- ARMOR condensing: PVC vent + condensate. Same diagnostics as residential NOBLE for ignition, fan, sensors
- Commercial sizing issue: if unit short-cycles or never satisfies demand, undersized for the application — engineering review needed
Common across all platforms
- Gas pressure: 7" WC NG, 11" WC LP under load. Manometer test by qualified contractor
- Condensate trap: primed and clear on all condensing units. Empty trap admits flue gas to room (CO hazard) and triggers vacuum-switch faults
- Sensor health: Lochinvar uses 12kΩ NTC thermistors throughout. Compare resistance at known temp against the service manual table
Bottom line
Combi: error code → DHW mode → flow → plate exchanger. Indirect: boiler-side first. Heat pump: mode + filter + condensate. Commercial: scale to size of operation, engage contractor. Almost all Lochinvar troubleshooting is contractor work — homeowner DIY is limited.