Replace the combustion fan assembly only if the motor spindle spins freely without audible grinding. Part number KM-060 for the 24 kW capacity model matches the original equipment impedance within ±5%–critical for flame sensor accuracy. Three-blade variants must align precisely to the burner manifold flange (use alignment tool 410-738).
Verify the diverter valve solenoid before swapping gaskets. O-rings on the hot-water outlet degrade at 8,000 operating hours; check silicone hardness with durometer reading below 70 shore A and replace with viton substitutes if surface cracks exceed 0.3 mm. Ignition electrode gap for optimum spark (0.7 mm) must be measured cold–wider gaps reduce efficiency by 11%.
Check the condensate neutralizer cartridge after winter operation; calcium deposits reduce pH below 6.5 and corrode the primary heat exchanger finned tubes. Use distilled white vinegar flush (30-minute soak) for visible scaling. Upflow models require bypassing the pressure switch first to prevent lockout during cleaning.
The expansion tank pre-charge should sit at 12 psi for installations under 30 feet elevation–overcharging voids warranty. Use a digital gauge with ±0.5 psi accuracy. Replace both Schrader valve core and entire tank if bladder integrity fails (discharge water when pressed).
Inspect the flame rod porcelain insulator under 10x magnification for hairline fractures. Clean with 1200-grit aluminum oxide sandpaper–abrasives coarser than 800 grit erode the platinum coating, increasing carbon monoxide output by 14%. Reinstall flame rod with molybdenum disulphide grease to prevent thread galling.
Understanding Your High-Efficiency Condensing Boiler’s Component Layout
Begin by locating the combustion chamber assembly near the base of the unit. This sealed system includes the gas valve, electrode, and flame sensor–critical for ignition and safety. Replace the electrode if sparking appears weak, using OEM part #30018890 for optimal performance. Verify the flame sensor’s conductivity with a multimeter; readings below 0.5MΩ indicate contamination or failure, necessitating cleaning or replacement (part #30018900).
The heat exchanger requires annual inspection for scaling, especially in hard-water regions. Flush it with a 5% citric acid solution, circulating for 45 minutes to dissolve mineral buildup. Avoid hydrochloric acid–it corrodes the stainless-steel coils. Check for leaks at the header connections; tighten fittings with a torque wrench (15 Nm max) to prevent thread stripping. If corrosion is present, replace the entire exchanger (part #30018910).
Key control components are clustered behind the front panel:
- PCB (part #30018920): Test input voltage (220-240V AC) and inspect for burn marks. Reset errors via the “Mode” button if the display shows E003-E005 (sensor faults).
- Pressure switch (part #30018930): Blow into the tubing to verify diaphragm function–audible clicks confirm responsiveness. Replace if silent or stuck.
- Flow sensor (part #30018940): Ensure the impeller spins freely. Calibrate via the service menu if hot water output fluctuates (±3°C threshold).
Exhaust and intake vents must be cleared of obstructions. Measure the concentric piping diameter (100mm for 24kW models); mismatched sizes reduce efficiency by up to 12%. Inspect the air pressure switch’s tubing for cracks–replace if brittle (part #30018950). For outdoor installations, add a condensation trap to the exhaust terminal to prevent ice blockage in sub-zero temperatures.
Circulation pump failure often mimics other issues. Check for humming without rotation–this indicates seized bearings (replace pump, part #30018960). Verify the pump’s rotational speed via the PCB diagnostics: 1800 RPM (±200) ensures adequate flow. For persistent noise, bleed the system through the bleed screw until air bubbles cease. Lubricate the shaft with food-grade silicone if replacement isn’t immediate.
Gasket integrity is frequently overlooked. Replace all seals during annual maintenance using:
- Combustion chamber gasket (part #30018970) – apply high-temperature silicone sealant.
- Heat exchanger sealing ring (part #30018980) – align precisely to prevent leaks.
- Front panel door gasket (part #30018990) – ensure compression for proper insulation.
Error codes E010-E012 often trace back to worn gaskets. Keep a moisture meter handy to detect internal condensation, which accelerates corrosion. Store spare components at ambient temperature to prevent O-ring degradation.
Locating Critical Elements in the Water Heater’s Exploded Schematic
Identify the combustion chamber assembly at the top center of the schematic–marked by item numbers 101-112. This cluster includes the igniter, flame sensor, and burner plate, critical for fuel ignition. Verify the placement of the flame rod (item 105) to ensure it extends directly into the burner’s flame path; misalignment here causes error codes E011 or E012. The spark electrode (item 104) should be positioned 3–5 mm from the burner surface for optimal ignition.
Trace the heat exchanger’s secondary coil (items 201-208) along the right side of the diagram. The stainless-steel finned tubes (item 203) must remain unobstructed; sediment buildup here reduces efficiency by up to 23%. The temperature sensors (items 210 and 211) attach to the inlet and outlet–swap them if readings fluctuate more than ±2°C, as faulty sensors trigger E037 or E051. Ensure gaskets (item 207) seal tightly to prevent leaks.
Focus on the blower motor assembly (items 301-306) at the top left. The impeller (item 302) should spin freely without scraping the housing–excessive vibration indicates bearing wear. Check the venturi tube (item 305) for cracks; air leaks here disrupt combustion ratios, leading to E515 errors. The pressure switch hose (item 306) must connect securely to the motor housing and remain free of kinks.
The control board (item 401) sits behind the front panel–remove the protective cover to access the PCB. Inspect capacitors for bulging or leaks, which cause erratic behavior or failure to power on. Locate the flow sensor (item 410) near the inlet pipe; clean its paddle wheel monthly to avoid false E016 alerts. Replace the board if corrosion is visible on the solder joints, particularly near the transformer (item 403).
Examine the condensate drain components (items 501-504) at the bottom. The neutralizer kit (item 503) must be installed above the drain pan (item 502)–overlook this, and acidic condensate will corrode the heat exchanger within 18–24 months. The U-trap (item 504) should maintain a 1.5-inch water seal; if dry, flue gases escape into living spaces. Replace cracked hoses (item 501) immediately to prevent leaks.
Step-by-Step Guide to Accessing the Heat Exchanger Assembly
Disconnect the gas supply line at the shutoff valve and cap the open fitting to prevent leaks. Remove the front panel screws (typically Torx T20 or Phillips #2) located at the corners–mark their positions if they vary in size. Lift the panel upward to disengage the internal clips, then tilt it forward carefully to avoid straining the control wiring harness. The primary combustion chamber lies directly behind, secured by four 12mm bolts; use a ratcheting wrench with a 10-inch extension to reach the lower fasteners.
Key Components to Inspect During Disassembly
| Component | Tool Required | Torque Specification | Common Failure Signs |
|---|---|---|---|
| Flame sensor | 5/16″ nut driver | 4-5 Nm | White residue, intermittent ignition |
| Ignition electrode | Needle-nose pliers | N/A (snap-fit) | Cracked ceramic, misalignment >3mm |
| Secondary heat exchanger | 12mm socket (swivel recommended) | 18-22 Nm | Corrosion pitting, scale buildup ≥1mm |
Slide the burner assembly forward on its rails after removing the two 10mm side brackets–do not force it if resistance is felt; check for hidden retaining clips near the gas manifold. The heat exchanger nest sits atop a foam gasket; peel it back gently to inspect for condensation drainage holes blockages (use a 3mm wire if necessary). Reassembly requires reversing the steps, ensuring the gasket seals fully–pressurize the system at 1.5x the rated working pressure (typically 15-20 PSI) and check for leaks with soapy water before restoring gas flow.
How to Spot and Swap Failing Igniters and Sensors in Gas Condensing Units
Before disassembling the combustion chamber, connect a multimeter in ohms mode to the igniter terminals. A functional ceramic ignition electrode registers 40–100 Ω; readings above 200 Ω or open circuits indicate burnout. For flame sensors, target 3–20 μA in DC microamps mode–values below 1 μA or erratic spikes confirm oxidation or contamination. Always detach the 24-pin connector and purge the gas line with nitrogen at 0.5 bar for 60 seconds before extracting the assembly to prevent pressure surges.
Step-by-Step Replacement
- Slide the lower cover panel loose by releasing the two quarter-turn fasteners at the rear edge.
- Disengage the M4 retaining screw securing the igniter bracket–mark its exact position with silver conductive paint to avoid re-calibration.
- Align the new electrode tip within 3.5 ± 0.5 mm of the burner orifice; angle it 12° toward the flame path.
- For sensors, apply dielectric grease (Dow Corning 56) to the metal collar threads to prevent future corrosion.
- Tighten all electrical connectors to 4 Nm torque using a preset driver; overtightening cracks the ceramic insulator.
- Power on the unit and observe the LED blink code sequence–steady amber confirms proper ignition; rapid red pulses signal persistent sensor faults.
- Run diagnostics via the control board’s service mode (hold MODE+UP+DOWN for 8 seconds) to verify 0.8–1.2 VDC at the flame signal terminal.