The Risk of Explosion of Electric Storage Water Heaters in Malaysia
By Mr Choo Wei Seng of ShowerTec Industries Sdn Bhd
Introduction
There are different types and ranges of water heaters in the Malaysian market. They mainly consist of (1) Electric Instant Water Heaters, (2) Electric Storage Water Heater, (3) Solar water Heater and (4) Industrial Heat Pump for commercial/hotel applications. Based on the number of units sold per annum in the Malaysia marketplace, the Instant Electric Water heater is always the best seller (500,000 units sold per year) followed by the Electric Storage Water Heater (80,000 units per year) and the Solar Water Heater (20,000 units per year).
From the above statistics, it is without doubt that the Electric Storage Water Heater is one of the popular methods of heating water in the Malaysian household, particularly for bathrooms in luxury condominiums, service apartments, SOHO and SOVO. The small size storage water heater (30 – 50 litres) were installed above the bathroom plaster ceiling without users noticing it at all. With increasing usage & long service life of Electric Storage Water Heater, some maintenance aspects of the safety measures are often overlooked & neglected. Recently there was an accident happened in February 2017, the bathroom of a luxury condominium was destroyed in an explosion caused by an Electric Storage Water heater. It looked like an explosion scene in a movie, buy it had actually happened in one’s life and it could happened to anyone else.
What could be possible the root cause of the explosions?
- Pressure relief & drain valve being/blocked spring mechanism jammed.
- Thermostat did not operate to stop heating element from heating.
- Thermal cut-out did not trip to stop heating element from heating.
What are the safety features of Storage water Heaters?
Pressure Relief Valve
This device is install at inlet, works as an expansion valve, it prevents build-up of water pressure to over Product’s Maximum Rated Pressure (usually 8.5 to 10.0 bar) by discharging the excess pressure through the overflow vent. It should not be removed from the heater. It is recommended that the Pressure Relief Valve be serviced by a qualified plumber at least once a year, and change to a new PRV unit every 5 years.
Thermostat
Thermostat is an Automatic Temperature Control System, which presets the temperature at the most economical setting of 70 degrees Celsius (° C) for normal usage. The green light indicator of product will light up when temperature is below this setting (usually 60°C), and goes off when temperature reaches this setting. This simple means, the thermostat is self-resetting , it connects the power supply to heater, and disconnects the power supply to the heater when the water temperature reaches 70°C.
Thermal Cut-Out
In the event the thermostat fails, the Overload Temperature Control System will cut off the electrical supply when the temperature reaches approximately 95°C. The red and green light indicators on the product will go off and the heater will stop functioning. This cut-off action is manual-resettable. However, the users are not allowed to reset it on their own. They will need to call a technician to check what is causing the thermal-cut to trip, and thus to remedy it accordingly.
Case Study / Last Accident Report
Water Heater Type: Storage Water Heater
Where: At a resort
When: December 2014
Accident: Water heater exploded – a non-fatal accident
Background
Water heater was installed around the middle of 2010. It was of a model with approval from the Energy Commission. It was purchased from the supplier and installed by the client’s technican. The water heater had a guarantee period of 6 months.
Findings
There were no records of maintenance. There was no RCD with a residual operating current of 10mA installed in the water heater circuit. The drain valve was found to be closed. (By referring to the water heater Operating Manual, the drain valve should always be in an open position).
The last user of the water heater did not/forgot to turn off the electricity supply to the water heater after using it.
The following safety features did not operate:-
- Pressure Relief and Drain Valve (the drain valve was closed)
- Thermostat
- Thermal Cut-Out
The majority of the Instant Water Heaters in Malaysia are Open Outlet Water Heaters, where the stop valve is installed at the inlet of the water heater. Hence there is no pressure exerted inside the heating canister of the product (Fig 1). The pressure is negligible for the Electric Instant Water Heater during operation and idling/standby. As for the Storage Water Heater, a Closed Outlet Water heater connect to many points in the bathroom, where the stop valve is actually at the point of use at the mixer tap of each location. For most of the time, it is on standby mode with pressure in the system exerted at 6-8 bars. Imagine a person who keeps on pumping a tyre with high pressure air. It will cause the tyre to explode into pieces and this could very well be fatal. It is the same case with the Electric Storage Water Heater when the Pressure Relief Valve (PRV) and Thermal Cut-Off both fail. It will slowly become a ‘tricking time bomb’ simply because water has been continuously heated up and turned into hot steam. When air turns into hot steam it can be compressed to 1,600 times of the original volume of water. Similarly, when the heater tank is pressurized until 25 to 30 bars, it will explode at any time.
To Improve the Safety of the Electric Storage Water Heater
- Regularly inspect the Thermostat operation and ensure that it is always in good working condition. This can be checked by observing the green light, whether it is turning on or off.
- Regularly inspect the Thermal Cut-Out operation and ensure that it is always in good/proper working condition. This can be confirmed when both the lights are off (which indicate the abnormal state).
- Regularly inspect the Pressure Relief Valve (PRV) operation and ensure that it is always in good working condition by lifting the lever to release water. This can prevent the spring in the PRV from getting jammed.
- Over a long period of usage, the internal parts of the heater tank that are in direct contact with hot water will accumulate scalings, that is, lime scale. In order to ensure that the heater works properly, it is important that the lime scale be removed from the Heating Element and Pressure Relief Valve. Refer to the cleaning procedures as outlined in the operation manual.
- Strictly follow manufacturer’s advice on the maintenance schedule. Do not assume that the product lasts forever after installation.
Conclusion
Electric Storage Water Heater users need to make sure that their Electric Storage Water Heater are maintained periodically.
The Pressure Relief Valve is recommended to be changed every 5 years, the discharge/drain area of PRV should not be blocked, and also, inspect the operation of thermostat regularly.
