How safe is your water heater? Here are 7 things to know to avoid deadly accidents

May 16, 2023

CNA Insider

Fire, electrocution or an explosion might happen in time, if your electric water heater has been wrongly installed. The programme Talking Point finds out what you can do to keep safe.

An instant water heater, one of two main types of electric water heaters. (File photo: iStock)

SINGAPORE: When Thakshnamurthy’s family moved into a seven-year-old resale flat in 2021, he did minor renovations but left the electrical system and water heater in place as everything looked “brand new”.

Then last November, fire broke out in the bathroom when his son was showering. His wife immediately went out to switch off the electricity at the mains while he got everyone else to leave the flat. No one was hurt.

The fire was due to improper installation of the connecting wires between the water heater and the circuit breaker, which eventually melted the wire insulation.

After that, Thakshnamurthy spent more than S$2,000 getting a licensed electrician to rewire his entire home and install a new water heater.

“It was very scary,” he told Talking Point as he showed programme host Steven Chia photos of the charred bathroom.

Besides fire, water heaters have been involved in explosions and even deaths from electrocution. How does one prevent such accidents? Chia spoke to four experts and found out seven things of note.

There are two main types of electric water heaters.

Instant, or tankless, water heaters, as the name implies, supply hot water instantly because the water flows through a heating element powered by electricity. They are mostly installed in Housing and Development Board (HDB) flats as they take up little space.

Storage water heaters, on the other hand, take up more space but provide a steady flow of hot water at higher pressures — ideal for rain showers. Water is heated and stored in these water heaters and reheated when needed.

No matter which one you buy, look out for the safety mark, advised service engineer Peck Choon Heng from Homeone Water Heater.

To be registered and sold in Singapore, all water heaters — as controlled goods — must have the mark. “Those without (the) safety mark aren’t allowed to be installed,” he warned.

Since 1985, all new homes must have a residual current circuit breaker (RCCB) installed. This device can cut off the power supply when it detects a leakage of electricity from an appliance or from wiring.

It is estimated — from a sample survey of about 1,800 HDB flats built before 1985 — that fewer than one per cent of such flats do not have an RCCB protecting the entire unit.

But the mere presence of the RCCB does not necessarily mean a water heater is safe to use. For example, the RCCB could be faulty or improperly installed.

“Test (to see) if the RCCB is working, then … test (to see) if the heater’s circuit is linked to this RCCB,” Peck advised.

To ensure safety at any residential premises, electrical work should be done by licensed electrical workers, while water service and sanitary plumbing should be done by licensed plumbers. But nine times out of 10, believes Peck, this does not happen.

“Simply google ‘water heater Singapore’. Most of the advertisements are (placed by) unlicensed (workers),” he charged, adding that shops selling heaters may also recommend unlicensed workers for installation work.

To obtain his licence, said Confucius Teo from Competent Electrician, he had to complete a course provided by the training arm of Singapore Power, go for an interview and sit a test given by the Energy Market Authority (EMA).

Including his time at polytechnic and on-the-job learning, it took about seven years. “Some can’t even get it after 16 years,” he said. “It’s very stringent.

“(The EMA is) handing you a licence (whereby) you could kill someone easily if you make a mistake.”

Customers can verify a licence on the EMA website, as with a plumber’s licence by using national water agency PUB’s search tool.

The installation of storage water heaters, for instance, must be carried out or supervised by a licensed plumber, who must submit a pre-installation plan to the PUB for approval.

This paperwork is the reason plumber Steven Tang charges about 10 per cent more than his unlicensed counterparts.

Teo, meanwhile, may charge double the amount quoted by unlicensed electricians for the same job, depending on how the water heater was wired previously. “We have a lot of things to check,” he said.

He lamented that many people choose unlicensed workers owing to the perception that “it’s a simple job — it just (involves) connecting wires”.

WATCH: What makes water heaters explode, catch fire or electrocute you (3:51)

When it comes to instant water heaters, the most common way in which electricity leaks is through use of a three-pin plug, said electrical engineer Wang Gucheng.

“In the recent deaths related to water heaters,” he cited, “the users used a three-pin plug.”

In December 2020, three family members in a Jurong flat died from electrocution after the cables in the three-pin plug that supplied power to their instant water heater had fused together.

A three-pin plug carries electric currents of 13 amperes, while “most of the water heaters (draw) about 14 to 20 amperes”, said Wang, the head of Temasek Polytechnic’s Clean Energy Research Centre.

He ran a test to demonstrate what would happen when there is an overload: When the temperature increased to 180 degrees Celsius, the insulator melted and the cables fused.

“If the earth (wire) melts with the live wire, then potentially the whole casing of the water heater will become live. That’s quite dangerous,” he said.

With normal usage, it typically takes a few years before overheating occurs, he added. But just a leakage of around 0.1 ampere — sufficient to light a bulb — passing through a human body can be deadly.

“It’s enough to kill one person,” he said. “The problem is, while you’re using a water heater, you’re wet. … Water is a good conductor of electricity.”

As Peck stated: “For instant heaters, the only contact point is (between) your hand and the heater, so there’s no other way for the current to flow in any direction other than your hand.”

Between 2014 and 2021, all five electrocution deaths in HDB flats were linked to water heaters.

Users should connect their water heaters to a double-pole switch instead, Wang advised. “This (switch) can take currents of up to 20 amperes, which is enough for a water heater.”

Also, wires in a three-pin plug “are very close to each other”, but a double-pole switch allows for “some distance” between cables, which is safer.

Compared to an instant heater, a storage heater’s pipework is joined to a mixer, so the chance of being electrocuted is very small, Peck said.

“It’s already connected to the ground, so if something happens, it’s very likely to just trip the (circuit breaker).”

But storage heaters are not without risk. In 2017, a storage heater in a Marine Parade condominium ruptured. The explosion was so strong that it shattered glass doors and windows.

WATCH: Hidden dangers of water heater — how to install it safely? (23:45)

Storage heaters are more elaborate because they are linked to multiple points, such as the shower areas and basins, unlike typical single-point instant heaters, said Tang, who is also secretary of the Singapore Plumbing Society.

A storage heater has safety features such as a pressure relief valve, which releases pressure when the water tank is overheated. “(But) if this doesn’t function, the water tank will be very dangerous,” he said. “It’ll cause (an) explosion.”

Few unlicensed plumbers understand the importance of the valve, he added, so some of them may not even install it.

Another important component is a drainpipe. “When a drainpipe in a wall is obstructed, it doesn’t allow the pressure to be released,” said Peck. “The pressure will continue to build up … and (the heater) will explode when it’s too high.”

As with the relief valve, he said unqualified workers may not even install a drainpipe.

Both types of water heaters can be a fire risk owing to their high electric current draw, which is about 3,000 watts, or 25 amperes, Peck said. In 2021, there were 17 cases of fires involving water heaters in homes.

When Chia had his storage heater checked, Peck found that the wires connected to it were too thin. Instead of measuring 2.5 millimetres square, the existing wires were 1.5 mm thick.

“When the current is high, (the wires) will overheat and will start to burn,” said Peck, who considered it a “fire hazard”.

On a day-to-day basis, users — especially those who have a storage heater — should switch on their heater 10 minutes before use, advised Peck. After use, they should switch it off to save electricity.

He also advised having heaters checked by someone qualified once every three years.

And now that Chia can do his own basic checks, he plans to “take a sniff around”. He said: “If you smell burning plastic, it might mean the wiring is overheating. And that’s not good.”

Watch this episode of Talking Point here. The programme airs on Channel 5 every Thursday at 9.30pm.