Lennox Furnace Code E205: Gas Valve Relay Short Fix

Last updated Sep 22, 2026 · By fixme.vip Editorial

Lennox furnace code E205: what it means

Lennox Code E205 means the furnace control board has detected that the gas valve relay contact is shorted, or that the gas valve is energized when the control expects it to be off. In plain terms: the circuit that switches the gas valve on and off is stuck, or is reading voltage at the valve at a time when there should be none.

Because an unintended open gas valve is a safety hazard, the board responds by locking out — it refuses to start an ignition sequence. On most Lennox SureLight/Unitary integrated boards this is a hard fault that holds until line power is cycled and the fault condition is corrected.

Check the number against your own board. The fault described above — gas valve relay contact shorted / gas valve energized when it should not be — is the manufacturer-documented meaning, and on Lennox boards it is numbered in the low-E200 range. The specific number, the wording, and the reset behavior can differ by board generation, so before you act on anything here, open the alert-code legend printed on your furnace’s blower-door label (or the installation manual for your board) and confirm that the code your furnace is showing carries this gas-valve-relay description. If the description on your label says something else — a rollout, a limit, a flame-sense fault — this is not your page.

This is a control-circuit fault, not a gas-supply or flame-proving problem. Do not confuse it with ignition or flame-sense codes.

Lennox furnace code E205: common causes, ranked by probability

1. Failed gas valve relay on the integrated control board — the relay contacts have welded or shorted, the single most common trigger for this code.
2. Shorted or pinched wiring in the gas valve harness — chafed insulation or a pinched wire back-feeding voltage to the valve circuit.
3. Faulty gas valve internal short pulling the circuit high when it should be de-energized.
4. Moisture or corrosion on the control board gas-valve terminals, bridging the circuit.
5. Miswired or back-fed control connection after a recent repair or component swap.

The board itself is usually the prime suspect because the relay lives on it, which is why E205 often ends in a control-board diagnosis.

How to fix Lennox furnace code E205: safe checks first

First: if you smell gas anywhere near the furnace, do not touch the breaker, the thermostat, or any switch. Leave the house, then call your gas utility’s emergency line or 911 from outside.

Given that this code specifically means the gas valve may be energized when it shouldn’t be, the safest homeowner response is to turn the furnace off at its service switch and leave it off until a technician has inspected it. Everything below is optional, stays outside the cabinet, and assumes there is no gas odor.

• Confirm the thermostat is calling for heat and set well above room temperature; replace thermostat batteries if it’s battery-powered.
• Check the air filter — a filthy filter won’t cause E205, but rule it out while you’re there.
• Verify the furnace switch and breaker are on. If, and only if, there is no gas odor, you may cycle the breaker off, wait 30 seconds, and back on ONCE to see whether E205 was a one-time glitch. If you’d rather not, that’s the safer choice — a technician can read the fault history either way.
• Confirm supply and return registers are open and unobstructed.
• Check the visible condensate line and drain outside the cabinet for backup or standing water, and report what you see to the technician.
• Make sure the blower access panel is fully seated — a loose panel can hold the door switch open.

Nothing inside the control compartment is a homeowner job. Do not remove the control-box cover, probe terminals, or disconnect wiring.

If E205 returns after one reset, stop. Do not repeat the reset. Switch the furnace off and call a licensed HVAC technician. A shorted gas valve circuit is exactly the kind of fault you don’t want to keep re-energizing.

How a technician will diagnose it

A qualified tech will typically:

• Read the fault history from the control board to confirm the code and check for companion codes.
• De-energize the furnace and inspect the gas valve harness for chafing, pinching, or moisture damage.
• Use a multimeter to check for voltage at the gas valve with the control commanding it off — verifying whether the relay is passing current it shouldn’t.
• Test the gas valve coil resistance to rule out an internal short in the valve itself.
• Inspect the board’s gas-valve relay terminals for corrosion, heat damage, or welded contacts.
• Confirm the diagnosis before replacing the board, since a wiring short or bad valve can mimic a bad relay.

You can sanity-check a quote: a tech who wants to swap the board should first show that the wiring and gas valve tested clean.

Symptom, cause and what to do

Lennox furnace code E205 repair cost

Honest US ranges, parts and labor:

• Diagnostic / service call: $90 – $180.
• Gas valve harness repair or reroute: $150 – $350.
• Gas valve replacement: $300 – $650 depending on model.
• Integrated control board replacement — single-stage or basic multi-stage: $400 – $750.
• Integrated control board replacement — variable-speed / modulating (SLP99V-class): $700 – $1,100 installed. Board replacement is the most common resolution for this code, since the relay is board-mounted.
• Visit where the fault doesn’t recur: you still pay the diagnostic fee, typically $90 – $180. A $0 bill happens only when the call itself is covered by a warranty or service plan.

If your furnace is within its parts warranty, the board or valve may be covered — you’d still pay labor, typically $150 – $300.

Related codes

• Code E204 — Lennox Furnace Code E204: Gas Valve Wiring Fix & Cost (a gas-valve wiring fault, distinct from a relay short)
• Code E125 — Lennox Furnace Code E125: Control Board Failure Fix & Cost (broader board failure)
• Code E131 — Lennox Furnace Code E131: Corrupted Control Parameters

Codes are only listed here when the meaning can be matched to Lennox’s own alert table, and numbering can still shift between board generations — verify any code against the legend on your furnace’s blower-door label before acting on it.

A note on rollout: a rollout-switch lockout is a separate and serious fault with its own alert number, and it is not this code. If your furnace’s own legend identifies the displayed code as a rollout, or if you see scorching, soot, or smell gas, shut the furnace off and call for service immediately.