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Error code reference

Honeywell Water Heater Error Code 8 Flashes

Power off failure.

Honeywell codesHoneywell water heater codes

Power off failure.

First step from the service manual

If the pilot flame is present when the control knob is set to the OFF position, replace the gas control valve/thermostat. If the pilot flame is not present, wait 10 minutes for thermopile to cool, then relight; if condition returns, replace the gas control valve/thermostat.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What 8 Flashes means on a Honeywell water heater

The 8 Flashes error code on a Honeywell water heater gas control valve indicates a power off failure. This fault is detected when the gas control valve's internal electronics sense that gas flow to the pilot or main burner has not properly shut off when the control knob is moved to the OFF position. The thermopile, a thermoelectric device that generates millivolt power from the pilot flame's heat, should stop producing voltage when the pilot is extinguished. If the control valve detects continued electrical output from the thermopile while in the OFF state, it interprets this as a shutoff failure and signals the fault.

The two primary scenarios that trigger this code are: a pilot flame that continues burning when the knob is set to OFF, or a thermopile that is still warm enough from residual heat to generate voltage even after the pilot has gone out. A functioning gas control valve should cut gas flow to the pilot completely upon command. If the pilot flame remains lit with the knob in the OFF position, the internal gas valve mechanism has failed to seal properly and the valve must be replaced.

If the pilot is confirmed to be out but the fault persists immediately after shutdown, the thermopile may still be radiating enough heat to produce a small voltage. The diagnostic procedure accounts for this by requiring a 10-minute cool-down period before relighting and retesting. If the 8 Flashes condition returns after allowing the thermopile to cool and relighting, the gas control valve itself is the confirmed failed component and must be replaced to restore safe operation.

Source: manufacturer service documentation.

Common causes of 8 Flashes

  1. 01

    Failed gas control valve internal mechanism

    Part replacement

    The internal valve mechanism has failed to stop gas flow to the pilot when the control knob is set to OFF, causing the pilot flame to remain lit. This is confirmed by observing an active pilot flame with the knob in the OFF position, and the gas control valve must be replaced.

  2. 02

    Residual thermopile heat generating voltage

    Wiring / connection

    Even after the pilot is extinguished, a hot thermopile can continue generating millivolt power for several minutes, which the control board may read as a failure to shut off. Waiting 10 minutes for the thermopile to cool before relighting will confirm if this is the cause.

  3. 03

    Gas control valve electronic fault

    Part replacement

    The internal electronics of the gas control valve may have developed a fault that causes it to incorrectly report or fail to execute the power-off sequence, even when the thermopile is cool and the pilot is not burning. Replacement of the gas control valve is the required repair.

  4. 04

    Pilot orifice or tubing issue preventing full shutoff

    Part replacement

    Debris or a compromised pilot orifice can sometimes allow a very small flame to persist after a shutoff command, sustaining thermopile voltage. Inspecting the pilot assembly for visible flame after setting the knob to OFF helps identify this condition.

See the test procedure for each cause

Frequently asked questions about 8 Flashes

What does 8 Flashes mean on a Honeywell water_heater?
Eight flashes on a Honeywell water heater gas control valve indicates a power off failure. This means the control system detected that gas flow or the pilot flame did not shut off correctly when the control knob was moved to the OFF position. It is a safety-related fault that requires immediate diagnosis and is typically resolved by replacing the gas control valve.
How do I fix the 8 Flashes error on my Honeywell water heater?
First, set the control knob to OFF and check whether the pilot flame is still burning. If the pilot remains lit, the gas control valve has failed to shut off gas flow and must be replaced. If the pilot is out, wait 10 full minutes for the thermopile to cool completely, then relight the unit. If the 8 Flashes code returns after that cool-down period, the gas control valve still needs to be replaced.
Is the 8 Flashes error on a Honeywell water heater dangerous?
Yes, this fault should be taken seriously because it indicates the gas control valve may not be shutting off gas flow properly. A pilot flame that continues burning when the unit is set to OFF represents a control failure that could pose a safety risk. Do not continue operating the water heater without addressing the fault, and if you smell gas at any point, leave the area and contact your gas utility company immediately.
How much does it cost to fix the 8 Flashes error on a Honeywell water heater?
The repair typically requires replacing the gas control valve, which generally costs between $150 and $400 for the part alone depending on the specific model. Adding professional labor for installation can bring the total repair cost to a range of $250 to $600 or more. In some cases, if the water heater is older, replacement of the entire unit may be more cost-effective than replacing the gas valve.
Will resetting my Honeywell water heater clear the 8 Flashes error code?
A simple reset will not permanently clear this error if the underlying fault still exists. The 10-minute cool-down period described in the diagnostic procedure is specifically intended to rule out residual thermopile heat as the cause before relighting. If the condition returns after the cool-down and relight, the error will continue to appear until the faulty gas control valve is replaced.

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