15th Oct 2026
Norcold 2118 oP LI Code and TMC Red Light
oP LI
Norcold 2118 oP LI Code and TMC Red Light
The Temperature Monitor Control (TMC) watches the boiler temperature with a thermocouple. If the boiler overheats, or the TMC circuit is open, the fridge shows oP LI and stops AC and propane operation. The TMC’s red light tells you which. Don’t reset the TMC lockout yourself. Work through the checks below first. The reset comes last, and we recommend a certified RV technician do it.
Before you start
- Where the TMC is. It’s the small black box behind the lower outside vent, wired to the power board’s LIMIT IN and LIMIT OUT terminals.
- Common causes of overheating: blocked or poor ventilation, a jammed heat deflector cap, parking off level (3° side to side, 6° front to back), or a failing cooling unit.
- Safety first. A solid red light can mean a leaking cooling unit. Do the leak checks in Part C before anything is reset. Resetting the lockout without finding the cause is a fire risk, so we recommend a certified RV technician do the reset.
Fits these models
The Norcold 2118 four-door, 2-way (120V AC and propane) refrigerator, including the IM (ice maker) and IMD (ice maker and dispenser) versions.
What you’ll see
oP then LI on the display. Then look at the TMC’s red light: solid, flashing fast (2 to 3 times a second), flashing slow (once a second), or off.
STEP 1
Rule out AC ripple
Dirty power from the converter can trip this code even when nothing is overheating. Set your meter to AC volts and measure across the fridge’s 12V DC supply while plugged into shore power. See how to check for AC ripple.
Is there more than 0.3 volts AC on the 12V DC supply?
Fix the converter first
The converter isn’t filtering its output, and the ripple can cause this code. Replace or repair the converter before you replace any fridge parts, then turn the fridge off and back on. If the code is still there, go to Step 2. Read AC Ripple: The Silent Killer of RV Refrigerator Power Boards.
STEP 2
Look at the TMC red light
Open the lower outside vent and find the TMC.
Is the red light on solid?
STEP 3
Is it flashing?
Watch the red light for a few seconds.
Is it flashing?
PART A · RED LIGHT FLASHING
Fast or slow?
STEP 4
Fast or slow?
Fast is 2 to 3 flashes a second. Slow is about once a second.
Is it flashing fast?
Open thermocouple circuit
Check that the thermocouple is plugged into the TMC’s T/C connector. If it wasn’t, plug it in; the TMC resets itself and the code clears. If it was plugged in, replace the thermocouple.
Low voltage to the TMC
Slow flashing means the TMC sees less than 9.5 volts. Get 10.5 to 15.4 volts to the TMC’s +12V terminal. Above 10.0 volts it resets itself and the code clears.
PART B · RED LIGHT OFF
Check the TMC wiring
STEP 5
Check the TMC wiring
Compare the TMC’s wiring to the wiring diagram.
Is it wired correctly?
Fix the wiring
Connect or repair it. If oP LI clears, you’re done; if not, start again at Step 2.
STEP 6
Is power reaching the TMC?
Measure DC volts between the TMC’s GND and +12V terminals.
Is there 12 volts?
STEP 7
Is the TMC passing power?
Measure between the TMC’s GND and +12V OUT terminals.
Is there 12 volts?
Replace the TMC
Power goes in but doesn’t come out. See Norcold 2117 / 2118 parts.
STEP 8
Is it reaching the board?
Remove the power board cover. Measure between the TMC’s GND terminal and the power board’s LIMIT_IN terminal.
Is there 12 volts?
Replace the power board
The limit signal reaches the board but it still reads open. It’s behind the lower outside vent, under a cover on the back of the fridge. Ask a tech if you’re not sure it’s the board.
Norcold Power Board 637082 / 636852 →The 2118 power board. Fits all 2118 models.Repair the blue limit-in wire
Fix the wire or connections between the TMC and LIMIT_IN. If oP LI clears, you’re done.
STEP 9
Is the board sending power?
Remove the power board cover. Measure between the gas valve bracket (ground) and the power board’s LIMIT_OUT terminal.
Is there 12 volts?
Replace the power board
The board isn’t sending power out to the TMC. It’s behind the lower outside vent, under a cover on the back of the fridge. Ask a tech if you’re not sure it’s the board.
Norcold Power Board 637082 / 636852 →The 2118 power board. Fits all 2118 models.Repair the TMC’s wiring
The board is sending power, so the red limit-out wire or the green ground wire to the TMC is broken. Repair the wire or connections. If oP LI clears, you’re done.
PART C · RED LIGHT ON SOLID
Check for a cooling unit leak before anything else
STEP 10
Inspect the boiler
Carefully remove the insulation canister and insulation from around the boiler. Look for yellow, powdery residue (leaking sodium chromate) and smell for ammonia.
Do you see yellow residue or smell ammonia?
Replace the cooling unit or the fridge
Those are signs of a leak. The cooling unit is sealed and can’t be repaired. Replace it, or upgrade to the 12V N20DC.
Nordic Cooling Unit 6618 (replaces 637080) →New replacement cooling unit for the Norcold 2118. 
Norcold N20DC 12V Refrigerator (19 cu. ft.) →Norcold’s 12V replacement for the 2118. No propane, no boiler, no cooling unit to fail.STEP 11
Test with litmus paper
Hold damp litmus paper around the boiler area.
Does the litmus paper show a leak?
Replace the cooling unit or the fridge
The cooling unit is sealed and can’t be repaired. Replace it, or upgrade to the 12V N20DC.
Nordic Cooling Unit 6618 (replaces 637080) →New replacement cooling unit for the Norcold 2118. Norcold N20DC 12V Refrigerator (19 cu. ft.) →Norcold’s 12V replacement for the 2118. No propane, no boiler, no cooling unit to fail.STEP 12
Reset the TMC lockout: have a technician do it
Only after Steps 10 and 11 show no leak and the cause of the overheating (ventilation, level or the heat deflector cap) has been found and fixed. The lockout has to be reset to get the fridge running again, but resetting it is a fire risk if the cause wasn’t found. We recommend a certified RV technician do the reset and test the fridge after it’s turned back on, on both AC and propane. Ask a tech if you need help.
Does it cool properly?
Repair complete
Keep an eye on it for the first few days. If oP LI comes back, turn the fridge off and don’t use it until it’s been inspected.
Replace the cooling unit or the fridge
Repeated lockouts also point to a failing cooling unit. The cooling unit is sealed and can’t be repaired. Replace it, or upgrade to the 12V N20DC.
Nordic Cooling Unit 6618 (replaces 637080) →New replacement cooling unit for the Norcold 2118. Norcold N20DC 12V Refrigerator (19 cu. ft.) →Norcold’s 12V replacement for the 2118. No propane, no boiler, no cooling unit to fail.Still stuck? ask a tech with your model, serial number and the code you’re seeing. We’ll confirm the part before you order.
Covers the Norcold 2118, 2118SS, 2118BK, 2118IM, 2118IMSS, 2118IMBK, 2118IMD, 2118SSIMD and 2118IMDBK. Based on the Norcold 2118 service manual (637026 Rev. B), fault code oP LI and the Temperature Monitor Control (TMC).