DIY Series 98: Joven Water Heater SA10E Not Working

Joven Water Heater SA10E Not Working

The Joven SA10E (3.6kW) is an instant water heater that uses a complex safety and control circuit to handle its 15A current. It does not wire a 10A thermostat directly to the heater; instead, it uses a PCB (Printed Circuit Board) with an EELS (Electronic Earth Leakage Sensor) to manage the switching safely. 

Joven SA10E Circuit Overview

The circuit for a 3.6kW Joven heater typically follows this path: 

• Main Power Inlet: 240V AC power enters through a 20A double-pole switch on your wall.
• EELS (Safety Board): Both Live and Neutral wires pass through a double-pole EELS system. If it detects a leakage of more than 10mA, it instantly cuts power.
• Flow Sensor (SFS): A magnetic sensor detects water flow. The heater will not activate unless water is flowing, preventing the element from burning out.
• Stepless Electronic Power Control: A knob on the front controls a Triac on the PCB. This electronic component acts as the "acting" switch, varying the power to the heater element based on your temperature setting.
• Thermostat with Safety Cut-Out: This is the "high-limit" thermostat. If the water exceeds a safe temperature (e.g., due to a PCB failure), it trips to prevent scalding and fire. 

Symptoms:

• No power at all when switch ON. Sometimes EELS (Green LED) will be ON for a while, then turn OFF again. The heater (Red LED) will not be turn ON, even temperature control knob is turn with water flow in.
• When press "Test/Reset" button, the EELS (Green LED) will be turn ON and then turn OFF immediately.
• Suspect the Main Control Board or thermostat malfunction.

Debugging:

• If you hear a mechanical click inside the unit when you press the "Reset" button, it confirms that either the EELS relay or the high-limit thermal cut-out has physically re-engaged.
• Since the EELS light is still staying off despite that click, here is the diagnosis:
• If the thermostat fails, it breaks the circuit completely. No power reaches the EELS board, so the light stays off.
• Use a multimeter to check for continuity across the thermostat. If it's "open" even after clicking, it must be replaced.

Findings:

• Checking the Main Control Board (Power Supply Board), found no issue.
• Trial and error to replace thermostat, see if it is the culprit. After changing thermostat, the Joven Water Heater (SA10E) resume back to normal.

Parts Sourcing:

• Found the thermostat written ATT S102, try to look for the original parts, but not available for sale at online store.

• Found another thermostat, KSD303 having same shape and size. Rating at 250VAC/10A, 150°C.

• Use Google Gemini to check compatibility. For a 10A application at 250VAC, both the ATT S102 and KSD303 are technically suitable, as 10A is a standard rating for both series. At this current level, the choice depends primarily on whether you need a direct manufacturer-specified replacement (ATT S102) or a more widely available, generic industrial alternative (KSD303)

• While some manufacturers may use a 10A thermostat in a 3.6kW water heater, it is only safe if it is part of a relay or contactor system. In such a setup, the 10A thermostat does not carry the full 15A–16A load itself but instead acts as a "trigger" for a higher-rated switching device. 

Photos:

• Joven Water Heater (SA10E) - bought in Year 2017

• Thermostat located at the top of the water tank

• Remove the thermostat (ATT S102)

• Replace with new thermostat (KSD303)

Tools Required:

• Multimeter
• Screwdriver
• Hex wrench (to remove thermostat)

Cost Involved:

• Thermostat (KSD303): US$1

How a 10A Thermostat Works with a 3.6kW Heater?

If your water heater was originally built with a 10A thermostat, it likely operates in one of the following ways:

• Indirect Switching: The 10A thermostat controls a contactor or relay that is rated for 20A or 25A. The contactor handles the heavy 15A current, while the thermostat only handles a very small control current.
• Safety Cutout Only: Some 10A thermostats are used strictly as a secondary safety limit (high-limit switch) designed to trip and stay off in an emergency, rather than cycling the heater on and off daily.
• Low-Voltage Controls: In modern digital or "smart" systems, the thermostat may operate on low voltage (e.g., 5V or 12V) to send a signal to an electronic board, which then switches the main power.

In the Joven SA10E, the 10A thermostat is likely used as a secondary safety trigger on the control board:

• It does not carry the 15A load directly.
• It sends a signal to the PCB/Relay/Triac to cut off the main power if things get too hot. 
• Typical thermal cut-out profile:
• Standard Thermostat (Auto Cut-Off) @ 55°C: Anti-Scald protection
• Manual Cut-Out @ 80°C–95°C: Secondary safety limit
• Thermostat Max Rating @ 150°C: For dry-burn protection in heating elements