Description
Direct replacement for WV8840B valves on A. O. Smith 1″ Insulation Tank (Natural Gas, 5″ W.C.) standing‑pilot tanks
The Honeywell/Resideo WT8840B1000 is a natural‑gas control valve that slips into the same 1‑in. immersion‑well cavity used by earlier WV8840B valves. No piping or bracket changes. A built‑in NTC sensor reads tank water up to 221 °F (105 °C) and holds the temperature you dial in, while a resettable ECO (Emergency Cut‑Off) stops the burner if the water ever exceeds 189 °F. Power comes from the pilot’s thermopile, so the control needs no external wiring or batteries. Eight specific LED error codes allow for fast water-heater triage.
This model serves as a replacement for:
- A.O. Smith 100112336
- A.O. Smith 9007884005
- A.O. Smith 316910-000
- A.O. Smith 321166-000
- Resideo / Honeywell WV8840B1042
- Resideo / Honeywell WV8840B1109
- Resideo / Honeywell WV8840B1110
Why choose this upgrade?
Direct WV8840/A.O. Smith Swap
½ ” NPT inlet × ½ ” inverted-flare outlet threads match WV8840 valves on most AO Smith tanks. No piping or bracket mods.
5 – 155 °F Dial Range & Water Limits
Front dial lets you pick shower temp down to 55 °F. An internal cut-out triggers a resettable ECO at 189 °F.
No Over Heating with NTC Sensor
The control algorithm and NTC sensor limits burner overshoot and minimizes water temperature overheating with temperature cut- out (TCO) function.
Resettable ECO
If the tank overheats, press the red ECO button and relight—no need to buy another valve.
Status‑Code LED
A status LED blinks once every 3 s in normal idle, strobes on a heat call, and reports eight specific error codes (2 flashes = low thermopile, 4 = high-limit trip, 5 = bad sensor, 7 flashes = electronics fault ,etc.).
Natural‑Gas Regulator Set to 5 in. W.C.
Handles heaters up to 75 ft³ /hr (≈ 75 kBTU/h) with a minimum of 30 ft³ /hr, matching most 30‑ to 50‑gal residential units.
Piezo Igniter and Larger Pilot Flame
Push-button spark lights the pilot. Stronger flame reduces outages and keeps the thermopile charged for stable operation.
Self-Powered Thermopile
Needs no 120 V feed—350–850 mV DC comes from the pilot’s thermopile, so the valve works through outages.
Smart Anti‑Scald Logic
Control algorithm minimizes water temperature overshoot, helping protect children and seniors from spikes.
Key Specifications
| Gas Type | Natural gas |
| Outlet Pressure | 5 in. W.C. (fixed) |
| Capacity | 30 – 75 ft³ / hr (≈ 30 – 75 kBTU/h) |
| Set‑Point Range | 55 – 155 °F (13 – 68 °C) |
| ECO Trip Point | 189 °F (87 °C) |
| Sensor | Integrated NTC, immersion‑well style (221 °F max) |
| Power Source | Thermopile (350–850 mV DC) from standing pilot |
| Mounting | Upright position, 1‑in. well, ½ in. NPT inlet × ½ in. inverted‑flare outlet |
In the box
- WT8840B1000 gas control valve
- Pre‑installed immersion‑well sensor
- Piezo igniter & status‑LED assembly
- Installer / owner instructions
FAQs
Why is the pilot not lighting?
Keep the pilot light button pressed 60 – 90 s so the thermopile reaches 350 mV. Letting go early starves the pilot magnet.
Why is pilot is lighting, but the LED isn’t blink
The thermopile isn’t hot yet. Wait ~30 s. If it still stays dark, pilot flame is too small, or the thermopile is weak.
What do the LED flashes mean?
- 1 blue flash = normal idle
- 2 red = low thermopile;
- 4 red = high-temp cut-out
- 7 red = internal fault—valve replacement needed
How do I fix the Status LED 2-flash code?
Low thermopile voltage: clean pilot or replace bad thermopile lead.
How do I reset a 4-flash high-limit trip?
Let the tank cool, verify probe contact & gas pressure, then relight. The limit resets automatically when temperature drops.
LED is dark—no blinks. Is the unit dead?
Check the pilot flame first. No LED + no pilot usually means a clogged pilot or dead thermopile, not a bad valve.
No status light and no pilot after water in the pan. Salvageable?
If the control gets wet, replace it. Moisture corrodes safety contacts.
Water too hot, LED 4-flash high-limit trip—do I replace the valve?
First check for scale bridging the sensor well and verify set-point. If limit keeps tripping, replace the valve. Internal ECO may be weak.
Is the valve natural gas only, or will it run LP?
The WT8840B series is natural-gas only (5 in. W.C.). Use the WT8840C (10 in. W.C.) for propane conversions.
Can I reuse the old CS8840 pilot assembly?
Yes. WT8840 is designed to pair with the matching CS8840 pilot; just verify clean orifice and 4″ W.C. pilot pressure.
Is the temperature sensor replaceable?
Yes. The NTC probe comes out with a clip. Always use the exact OEM sensor to keep the cut-out calibration.
Will the bracket carry different insulation depths?
This B1000 version is for 1-in. tank insulation. Thicker R-value tanks need the longer-spud WT8840B1500.
Does the knob have to be OFF before pulling the inlet plug to gauge pressure?
Yes. Put the gas switch in OFF before opening the test tap, then leak-check after re-sealing.
