Description
A failing hot water cylinder thermostat either lets the water run cold (no element switching) or runs the cylinder past its safe set point until the temperature pressure relief valve dumps water on the floor. Both faults are obvious once they happen, and both are solved by swapping the thermostat rather than the cylinder.
This is a replacement 11 inch (280mm) stem thermostat for domestic hot water cylinders, rated 20A at 250V AC. It is the standard part for cylinders that use an 11 inch thermostat pocket, with an adjustable temperature range of 40 to 80 degrees Celsius and an over temperature cut out at approximately 85 degrees Celsius. Common equivalent codes include ST111, VK4354, EUTVK4354, EUT111, and EUT11STEME.
Key Features
- 11 inch (approximately 280mm) stem thermostat with clip
- Temperature range: 40 to 80 degrees Celsius
- Rating: 20A at 250V AC
- Over temperature cut out (safety reset) at approximately 85 degrees Celsius
- Equivalent codes: ST111, VK4354, EUTVK4354, EUT111, EUT11STEME
- Replaces the obsolete ST series with smaller mechanism and added over temperature cut out
- Suits domestic hot water cylinders with an 11 inch thermostat pocket
Product Details
- Type: Stem thermostat with mounting clip
- Stem length: 11 inch (approximately 280mm)
- Temperature range: 40 to 80 degrees Celsius
- Over temperature cut out: approximately 85 degrees Celsius
- Electrical rating: 20A at 250V AC
- Compatible cylinder type: Domestic, mains pressure and low pressure (per cylinder design)
- Operating differential: approximately +/- 6 to 8 degrees Celsius
- Material note: For copper cylinders, a copper stemmed thermostat should be used to prevent galvanic corrosion. Check stem material against your cylinder before ordering.
- Also known as: ST111, VK4354, EUTVK4354, EUT111, EUT11STEME
Compatibility
This 11 inch stem thermostat fits domestic hot water cylinders that have an 11 inch (280mm) thermostat pocket. The STK style replaces the older obsolete ST series, with a smaller mechanism and an added over temperature cut out that allows use in a wider variety of applications, especially mains pressure cylinders. It is suitable for most New Zealand domestic vitreous enamel and copper cylinders that use the 11 inch stem format. The verified application list appears in the table at the end of this description. For dairy cylinders that operate above 100 degrees Celsius, use the higher range Dairy 11 inch thermostat instead (60 to 110 degrees Celsius). Always measure the existing stem before ordering.
How to Use and Installation Notes
- Switch off the cylinder at the wall isolator and confirm power is dead at the thermostat with a tester.
- Drop the cover plate to expose the existing thermostat and note the wiring positions before disconnecting.
- Disconnect the wiring from the failed thermostat.
- Release the retaining clip and withdraw the old 11 inch stem from the thermostat pocket.
- Slide the new stem fully into the pocket so the temperature sensing element sits deep enough to read cylinder temperature accurately.
- Refit the retaining clip so the thermostat cannot vibrate loose.
- Reconnect the wiring to the same terminals as before.
- Set the dial to your preferred temperature (60 to 65 degrees Celsius is typical for hot water cylinders to balance scald safety and Legionella prevention).
- Refit the cover plate, restore power, and verify the element switches on and off correctly as the cylinder heats and cools.
Fitting and Safety Note
Related Parts and Collections
Verified Compatible Models
| Domestic hot water cylinders with 11 inch pocket | Standard vitreous enamel cylinders |
| Mains pressure cylinders (where compatible) | Low pressure cylinders |
| Copper cylinders (copper stem version required) | Older Rheem domestic cylinders |
| Older Mainline / Vulcan / Triumph cylinders | Cylinders previously fitted with ST111 |
| Cylinders previously fitted with VK4354 | Cylinders previously fitted with EUT11STEME |
| Aqualine 11″ Thermostat TH11 | Domestic Hot Water Cylinders with 11" Thermostats |