Lennox E250: limit switch circuit open

Furnace control display or LED

E250

“Limit switch circuit open.”

Printed on 19 model series · 19 documents

SL280*V, SL280*NV, SL297*NV, SLP98*V, SLP99*V, EL296*V, EL296*E, EL297*V, EL297*E, EL280*E, EL195*NE, EL196*E, EL180*NE, ML180*, ML193*E, ML196*E, ML296*V, ML297*V, G71MPP · 508559-01 p. 30; 508561-01 p. 37; 508585-02 p. 50; 506610-01 p. 63; 508589-02 p. 46; 1126-L5 p. 17; 1246-L10 p. 13; 508583-01 p. 53; 508577-02 p. 45; 1901-L1 p. 14; 508575-02 p. 47; 508573-01 p. 46; 508545-01 p. 29; 508547-01 p. 49; 508565-01 p. 43; 508569-01 p. 46; 508521-01 p. 44; 508907-01 p. 48; 506509-01 p. 66

Technician

What it means

E250 means the control sees the limit switch circuit open. Most Lennox tables give the same action: check for proper firing rate on the furnace, make sure there is no blockage in the heater, and check for proper air flow. If the limit does not close within 3 minutes, the unit goes into a 1-hour soft lockout; it resumes normal operation after the fault clears 508585-02, p. 50. The SLP99DFVK table puts the action in fewer words: “Check why limit is tripping, overfired, low air flow.” 508589-02, p. 46.

The same tables have a separate code for a limit that stays open: E274, “Soft lockout - Exceeded maximum number of recycles. Last recycle failed due to the limit circuit opening or limit remained open longer than 3 minutes”. Its action starts “Shut down system. 1-hour soft lockout.” 508585-02, p. 51.

Lennox’s thermostat alert 250 is “GF Primary Limit Switch Open”, priority Service Soon. Its description says that if the limit switch does not close within three minutes, the unit goes into a 60 minute soft lockout (Watchguard mode). Its checks are high gas pressure; low supply air because the system is plugged or restricted, with a dirty air filter or blockage in duct work as the examples; the firing rate; and zone dampers that do not work 100017, p. 22. Lennox’s documents do not say that alert 250 and display code E250 report the same event.

Check these first

Lennox’s owner’s manuals have no code table and give no steps for E250. What they give is a general list for a unit that will not operate, to work through before calling a Lennox service technician. In the SLP99DFVK manual the order is:

Check that the electrical disconnect switches are ON 508590-01, p. 5.
Check the room thermostat for proper setting 508590-01, p. 5.
Replace any blown fuses or reset circuit breakers 508590-01, p. 5.
Check that the gas valve is ON 508590-01, p. 5. Its switch is behind the outer access panel; the manual’s gas valve steps set the thermostat to the lowest setting and turn off all electrical power to the unit before that panel comes off, and the switch is moved by hand only, never with tools 508590-01, p. 4.
Check that the air filter is not plugged, which would limit air flow 508590-01, p. 5. The SLP99DFVK manual says its filters are installed external to the unit, should be inspected monthly, and that a filter must be in place when the unit is operating 508590-01, p. 4. Before any service or maintenance, it says to turn the electrical power to the unit OFF at the disconnect switch 508590-01, p. 2.
Check that gas is turned on at the meter 508590-01, p. 5.
Check that the manual main shut-off valve is open 508590-01, p. 5.

Then record the model and serial number from the nameplate and call 508590-01, p. 5. The list is not tied to any code. More on it, and on how other Lennox manuals word it: owner checks before a service call.

If the furnace overheats or the gas supply fails to shut off, the manual says to shut off the manual gas valve to the furnace before shutting off the electrical supply 508590-01, p. 4.

When to call a licensed technician

Checking the firing rate, looking for blockage in the heater and checking the air flow 508585-02, p. 50.
The alert guide’s further checks for alert 250: high gas pressure, restrictions in the system such as blockage in duct work, and zone dampers that do not work 100017, p. 22.
Any work inside the furnace. The owner’s manual leaves maintenance to a licensed professional service technician 508590-01, p. 5.
The furnace still will not run after the checklist 508590-01, p. 5.
E250 keeps coming back after it clears. The owner’s manuals give no step for that; these pages send it to the technician.

Notes for different models

Series or document	Code	Wording	Source
E-code tables of the SL280, SL297, EL280, EL296, EL297, EL180, EL195, EL196, ML180, ML193, ML196, ML296 and ML297	E250	“Limit switch circuit open.”	508585-02, p. 50; 508569-01, p. 46; 508521-01, p. 44
SLP98V, SLP99V, G71MPP	E250	“Limit switch circuit open - Refer to troubleshooting in installation instruction.” Action: “Check why limit is tripping, overfired, low air flow.”	508589-02, p. 46; 506610-01, p. 63; 506509-01, p. 66
SL280UHV, 2011 instructions	E250	“Limit switch circuit open - Refer to troubleshooting.”	506763-01, p. 63
ML180UHVK, compact table	E250	“PRIMARY LIMIT SWITCH OPENED”, in the group “GAS VALVE/PRESSURE SWITCH/LIMT FAULTS (wait for recovery)”	508547-01, p. 26
Lennox thermostat alert table	250	“GF Primary Limit Switch Open”, Service Soon	100017, p. 22

Furnaces with a red LED show an open limit as a flash count. The documents do not translate flash counts into E-codes; these rows only show where the limit appears in the flash tables:

Table	Flashes	Wording	Source
13-flash table, board 103217-03	7	“Primary or Secondary Limit Open or Watchguard Mode - Limit Switch Open longer than 3 minutes”	507966-04, p. 40
9-flash tables: ML193UH, ML195UH, ML180DF	4	“Primary limit switch open.”	507121-01, p. 39; 507268-03, p. 39; 507326-01, p. 21
ML296UHV installation instructions	4	“Primary limit, secondarylLimit, or roll-out switch open” (as printed)	507869-04, p. 46
ML296DFV(X) service literature	3 and 4	3: “Low-fire pressure, rollout or limit switch open.”; 4: “Primary limit switch open.”	1904-L1, p. 8