Why is there no hot water?

Water heater not working? Start with power and switches

These checks follow the power and flow causes on Ariston's Singapore support page, used here only as an example of a manufacturer's list. Stop if anything looks damaged or the power trips again.

1. Check the heater switch. Make sure the power switch for the water heater is turned on.
2. Check the selector knob. On an instant heater, check that the selector knob is turned on, not just the wall switch.
3. Look at the DB box. Check the distribution board for a tripped RCCB or MCB. If it trips again when you switch it back on, leave it off and arrange power trip repair.
4. Try another hot tap. Run hot water at a different tap or shower, and note which outlets stay cold so you can tell the technician.
5. Open the stop-cock fully. For an instant heater, make sure the stop-cock valve is fully open, because low flow can stop it heating.

EMA explains that an RCCB cuts off electricity when it detects a current leakage that may lead to an electric shock, and faulty appliances are one cause.

Instant heater faults

If the water flow is too low to trigger the flow switch, an instant heater stays cold even with the power on. Ariston's Singapore support page, for example, lists these causes for an instant heater that gives only cold water.

Other brands' manuals list their own checks, so check the manual for your model.

Storage heater element and thermostat

Ariston's support page lists these causes when a storage heater gives only cold water:

• The electric switch is not on.
• The thermal cut-out has activated, and the safety device needs to be reset.
• The thermostat is not fitted properly on the element.
• The heating element is cut off or short-circuited, and needs replacing with its gaskets.
• There is no power supply.

If the circuit breaker cuts out when you switch the heater on, Ariston points to an incorrect electrical power setting or an earthed element, which should be tested and replaced if necessary.

Replacing an element or a thermostat is technician work. For repair options, see water heater repair. The cost depends on the fault and the parts, so ask what the quote includes.

Low flow or lukewarm water

If you find the water heater not hot enough, Ariston's list for insufficient hot water points to the power supply, a defective thermal cut-out or the electronic card. Ask a technician to test the cut-out and the card. In a storage heater, frequent short on and off cycles or noise while heating point to scale on the element, which needs cleaning or descaling.

For weak flow at an instant heater, Ariston's list covers the stop-cock, the inlet pressure and the mesh filter. If flow is weak at other taps too, see low water pressure at home.

Who to call: plumber, electrician or the manufacturer

If the heater is under warranty, contact the manufacturer first. Ariston's support page, for example, lists a hotline and a WhatsApp channel, open Monday to Friday, 9am to 5pm.

Electrical faults, such as tripping or no power at the heater point, need an LEW. EMA requires electrical works at consumers' premises, including repair and replacement, to be done by LEWs. You can check a licence on EMA's ELISE portal.

PUB lists replacing the pipe between a stop valve and an instantaneous water heater as simple work a handyman may do. Storage heater pipework is not on that list, so it needs a PUB Licensed Plumber. Engaging an unlicensed plumber for regulated works has been an offence since 2018. PUB also advises asking for itemised quotes and getting at least three.

Prices depend on the job. See plumbing costs for how companies publish theirs.

When to stop and call a professional

Stop using the heater, keep it switched off and call a professional if:

• The power trips when the heater is on.
• You smell burning or see sparks.
• Water leaks from the casing.
• There is rust on the heater.
• The heater is old and faults keep coming back.

Ariston says rust or leaks at the cover, bracket or flange point to corrosion that has perforated the boiler, and the heater should be replaced. For more signs, read water heater warning signs.

Questions