AGA hotplate not reaching temperature (mechanical thermostat models)
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
- Boiling plate will not boil / simmer plate too cool or too hot
- One hotplate works, the other does not
- Hotplate cycles at the wrong temperature
Likely causes
What is usually behind it
- Liquid-filled control thermostat failed or out of calibrationmost common
- Manually resettable overheat thermostat trippedcommon
- Element failure (one of the three internal circuits)common
- Rotary control switch failureless common
Diagnostics
How a technician diagnoses it
Our technicians follow the factory diagnostic path for this fault.
- 1R7 hotplate targets: boiling plate 340 °C / 644 °F, simmer plate 240 °C / 464 °F.
- 2Access: remove the four chrome buttons and stay nuts, lift the top plate and prop it with hob support bars (AE4M280399).
- 3The rotary control switch, control thermostat and overheat thermostat are located behind the front plate area; both hotplate element plates have manually resettable overheat thermostats that switch the neutral side.
- 4Check the thermostat phial location — a displaced phial causes wrong-temperature symptoms with a good thermostat.
- 5Simmer spot behaviour is normal-by-design: the 200W element runs permanently while the 2100W element cycles on the thermostat.
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.
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.