AGA thermocouple open circuit or drifting
Common issue — here is how we diagnose it, which parts are usually involved, and when to call a pro.
- Common
- Professional repair only
- Cast Iron Range
Symptoms
What you will notice
- Zone overheats or never reaches temperature
- Error 020–024 or 060–100
- Zone locks out intermittently
- Two thermocouples in one zone report very different temperatures
Likely causes
What is usually behind it
- Thermocouple open circuitmost common
- Thermocouple that tests OK cold but drifts or opens at operating temperaturecommon and easily missed
- Thermocouple not fully plugged into the user control panelcommon
- Thermocouples cross-connected on the back of the TCU (causes overheat code 120–124)installation/repair error
Diagnostics
How a technician diagnoses it
Our technicians follow the factory diagnostic path for this fault.
- 1Duplex thermocouples: 4 wires at the plug. Each thermocouple is one green + one white conductor — measure across green and white.
- 2Do NOT clear a thermocouple on a cold bench test alone. Units have tested fine at room temperature and gone open circuit hot.
- 3Verify the tip is located correctly in its bracket on the element; on the hotplates the thermocouple attaches to the element with a bracket.
- 4Confirm the TCU rear connections match the imprinted zone abbreviations: BO, HS, SS, SO, RO.
- 5Refit the rubber bungs in the thermocouple conduits after replacement — missing bungs cause user-panel overheat (code 139).
Safety & DIY disclaimer
Guides on this site are for information only. Appliance repair involves 240V electricity, gas connections, refrigerant and heavy cast-iron parts — anything you do yourself is at your own risk and can damage the appliance or cause injury. The safe option is to book a qualified technician.
Parts
Parts usually needed
We confirm the failing part with diagnostics before replacing anything.
Fault codes
Related error codes
Coverage
Appliances affected
Keep reading
Related AGA problems
Frequently asked questions
Can I fix this myself?
Professional repair only. This fault involves gas or 240V electrical components — diagnosis and repair should be done by a licensed technician.
How much does it cost to fix this issue?
Every visit starts with diagnostics and a written estimate — the diagnostic fee applies toward your repair when you proceed. We never start work without your approval.
Not sure? We diagnose first.
Book a diagnostic visit — you get a written estimate before any work, and the diagnostic fee applies toward your repair.
Mon–Sun 8:00AM–8:00PM
Independent service company — not affiliated with or authorized by AGA / AGA Rangemaster (Middleby). We repair out-of-warranty AGA appliances.