Overheating Indicator for Water Pipe

By M.K. Chandra Mouleeswaran & S. Santhosh Kumar

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The hot water pipe from the water geyser of your bathroom may burst if it gets overheated and is left unattended. This overheating indicator circuit monitors the temperature of the water pipe. If the temperature of the pipe goes above a certain limit, it flashes an LED.

Overheating indicator circuit

The circuit uses a small sensor with an inbuilt thermostat. It is actually an automatically resettable thermal switch that operates whenever its temperature exceeds the set limit. It is available in two versions, viz, normally open (N/O) and normally closed (N/C).

Circuit for over-heating status

Three different types of circuits are described here. The first circuit shows over-heating status of the pipe through LED1. As soon as the temperature of water pipe rises above the preset limit, the N/O contact of the thermostat closes and current flows through LED1. The LED1 glows to indicate that the temperature of the water pipe has exceeded.

Overheating indicator circuit
Overheating indicator for the pipe through LED

The circuit below gives an aural indication of over-heated pipe through piezo buzzer PZ1. When the temperature of the pipe goes above the set limit, the N/O contact of the thermostat closes to sound the piezo buzzer.

Circuit for aural indication of overheated pipe
Circuit for aural indication of overheated pipe
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The N/O version closes the switch upon the set limit, while the N/C version opens the switch. The thermostat automatically resets as soon as the temperature returns to the initial state. It can be directly mounted on the part to be monitored.

The circuit below gives an audio-visual indication through piezo buzzer PZ2 and LED2. When the temperature of the pipe goes above the set limit, the N/O contact of the thermostat closes to light up LED2 and sound piezo buzzer PZ2.

Circuit for audio-visual indication
Circuit for audio-visual indication

The sensor is available in various temperature settings. The temperature limit is specific from 70°C up to 110°C for each model number. For instance, the type 67L080 will change state at around 80°C+5°C. You can select the type suitable for your requirement. Use a three-core wire for connecting switches to the relay.

Circuit operation

The circuit uses very few components. Also, it does not require a separate power supply and can be connected to the power supply of the water heater suitably. Normally, the circuit remains idle and no current flows through it.


The project was first published in August 2010 and has recently been updated.

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