Immersion Thermostats

Shop genuine immersion thermostats for hot water cylinders, immersion heaters and Megaflo systems. This range includes replacement rod thermostats, resettable immersion thermostats, thermostat cut-out assemblies and cylinder temperature controls for Heatrae Sadia, Baxi and compatible water heating systems.

An immersion thermostat controls the water temperature inside the cylinder by switching the immersion heater on and off as required. Many models also include a resettable safety cut-out to help protect the system from overheating.

Whether you are replacing a faulty thermostat, repairing a Megaflo cylinder or carrying out preventative maintenance, Heatraq supplies reliable immersion heater controls with fast UK delivery and technical support.

Related immersion heater parts

If you are carrying out a wider repair, you may also need replacement immersion heaters, an element plate assembly, or broader thermostats and thermal cut-outs for water heater safety controls.

Replacement Immersion Thermostats for Megaflo and Hot Water Cylinders

Immersion thermostats are essential control components in electric hot water systems. They help maintain the correct water temperature, improve system safety and prevent the immersion heater from running continuously. If a thermostat fails, the cylinder may stop producing hot water, overheat, trip repeatedly or fail to maintain a consistent temperature.

This collection includes genuine Heatrae Sadia immersion thermostat parts, including Megaflo immersion thermostats, resettable rod thermostats and combined thermostat and thermal cut-out assemblies. Where available, product pages include part numbers, previous product codes and compatibility notes to help engineers and homeowners identify the correct replacement.

Choosing the Correct Immersion Heater Thermostat

Immersion thermostats are not universal. The correct part depends on the cylinder model, thermostat length, control type and whether the system requires a standard thermostat or a combined thermostat and thermal cut-out assembly. Always check the existing part number, cylinder data label and manufacturer documentation before ordering.

If your immersion heater keeps tripping, produces no hot water or heats the water excessively, the thermostat may be faulty. However, similar symptoms can also be caused by a failed immersion element, wiring fault or scale build-up, so the system should be checked by a qualified professional.

What’s the difference between immersion thermostats and thermostat cut-outs?

An immersion thermostat controls the temperature of the water inside the cylinder, switching the heater on and off as required. A thermal cut-out is a safety device that disconnects power if the system overheats. Many modern immersion thermostats combine both functions into a single unit for safety and convenience.

Popular Immersion Thermostats

Some of our most commonly replaced immersion thermostats include the Heatrae Sadia 95612026 Megaflo thermostat and combined thermostat and cut-out assemblies such as the 95612720 and 95612719.

Immersion Thermostats FAQs

What does an immersion heater thermostat do?

An immersion heater thermostat controls the temperature of the water inside your cylinder. It switches the heating element on and off to maintain the set temperature and includes a safety cut-out to prevent overheating.

Why does my immersion heater keep tripping the reset button?

If your immersion heater thermostat keeps tripping, it may be due to overheating, a faulty thermostat or a failing heating element. Repeated tripping is a common sign that the thermostat needs replacing.

How do I reset an immersion heater thermostat?

Most immersion heater thermostats have a reset button located behind the cover. If the safety cut-out has tripped, pressing the reset button can restore operation. If it continues to trip, the thermostat may be faulty and need replacing.

How do I know if my immersion heater thermostat is faulty?

Common signs include no hot water, water that is too hot, or the heater constantly switching on and off. A faulty thermostat can also cause the system to trip or fail to maintain a consistent temperature.

Can a faulty thermostat stop an immersion heater from working?

Yes — if the thermostat fails, it may prevent power from reaching the heating element, resulting in no hot water even if the element itself is still working.

What temperature should an immersion heater thermostat be set to?

Most immersion heater thermostats are typically set between 55°C and 65°C. This provides efficient heating while helping to prevent overheating and reduce the risk of scalding.

Are immersion heater thermostats universal?

No — immersion heater thermostats vary in length, compatibility and design. It’s important to choose a thermostat that matches your immersion heater and cylinder specification.

Can I replace an immersion heater thermostat myself?


Replacing an immersion heater thermostat is a straightforward task for a qualified professional. For safety, always ensure the power supply is isolated before attempting any work.

Do you supply immersion heater thermostats for different cylinder types?

Yes — we supply a wide range of immersion heater thermostats suitable for various cylinder types, including domestic and commercial hot water systems.

Do you offer next day delivery on immersion heater thermostats?

Yes — we offer next working day delivery on immersion heater thermostats for orders placed before 2pm, helping you restore hot water quickly.