Water heater not heating? The likely causes (and quick checks)
Cold shower out of nowhere? Check external power safely, then learn the storage and instant-heater faults—from elements and thermostats to flow sensors—that need proper diagnosis.
Few things ruin a morning like a cold shower you weren't expecting. The good news: a water heater that's stopped heating usually comes down to a manageable diagnostic shortlist. Here's how to work through them — safely — before you reach for the phone.
Safety first: a water heater sits on mains power in a wet room. Switch it off at the breaker before touching anything, and never open the unit yourself. The checks below are the safe, outside-the-unit ones.
1. Power — is it actually on?
Check the heater's isolator switch and the breaker (MCB) in your distribution board. A water heater draws a lot of current, so its breaker can trip. If there is no moisture, burnt smell, unusual heat or tingling, and the board is dry and safely accessible, reset the breaker once; if it trips again immediately, stop and get it looked at — that's a fault, not a fluke, and it may need a proper power-trip diagnosis rather than another flip of the switch.
2. Protective devices: ELCB is not the thermal cutout
An earth-leakage device and an over-temperature cutout protect against different hazards. Some instant heaters provide an external user test or reset control; storage-tank thermal cutouts are often behind a cover near the element. Never open the unit to reach one. Use an external control only as the exact model manual directs, and stop if it trips again. Singapore's CPSO water-heater guidance also says the heater must be directly wired through a double-pole switch by a Licensed Electrical Worker.
3. Faulty heating element
The element is what actually heats the water, and it's the most parts that can fail. Mineral or sediment buildup can also reduce heat transfer, but Singapore's water hardness varies: PUB's current drinking-water report should not be turned into a blanket "hard water" diagnosis. Signs of an element or supply problem include a unit that has power and isn't tripping, but the water stays cold or takes far longer than usual to warm. This is a classic no-hot-water repair and needs a replacement element.
4. Thermostat fault
The thermostat tells the element when to heat. If it fails, you get either no heating at all, or water that's scalding or barely warm with no in-between. Also a part-replacement job.
5. Instant-heater flow or inlet problem
A single-point instant heater may not energise if water flow or inlet pressure is below its operating threshold. A blocked inlet mesh filter, restricted showerhead or hose, faulty flow sensor, booster-pump fault, or control error can all leave the water cold. Do not open the heater: check only the stop valve and user-cleanable items named in the manual, then book diagnosis if flow is normal and the heater still does not start. Ariston Singapore's official troubleshooting page lists low flow, inlet pressure and a blocked mesh filter among instant-heater causes.
When it's time to replace, not repair
A confirmed perforated storage tank or cracked sealed heating chamber usually means replacement. For an element, thermostat, valve, sensor or control fault, compare the written diagnosis, parts availability, remaining warranty and compliant replacement quote. If yours is already dripping rather than just cold, our guide to what causes a water heater to leak walks through whether it's a fitting or the tank itself. Use the quick guide below to decide which way to lean.
| Symptom | Lean repair | Lean replace |
|---|---|---|
| Age | Age does not prevent repair when the diagnosed part is supported | Age plus obsolete parts, poor condition and no useful repair warranty |
| Cold or slow water | Worn element or thermostat on a newer unit | Tank/chamber failure or unsupported internal parts |
| Leaking | Loose fitting or connection | Tank or body itself is leaking |
| Tripping | Qualified diagnosis finds a repairable circuit or component fault | Repeated trip: leave off until assessed; replacement depends on diagnosis |
Our brand comparison helps you pick, or browse instant and storage heaters in the catalogue. When you're ready, our water-heater replacement service handles the swap and safe disposal of the old unit.
The takeaway
Start with external indicators, the heater switch and the DB breaker from a dry location. Do not open the unit or keep resetting a protective device. Storage element and thermostat faults, instant-heater flow controls, and repeated trips need qualified diagnosis. If the breaker is the part that keeps going, it's worth reading up on what makes an HDB circuit trip before assuming the heater is at fault. If a quick reset doesn't bring the heat back, don't keep cycling it; WhatsApp us the brand and a photo and we'll diagnose it properly. See our water-heater service for what's involved.
Frequently asked questions
- Why is my water heater suddenly not heating in Singapore?
- Common causes include loss of power, a protective device operating, a failed element or thermostat, and—in an instant heater—low flow, a blocked inlet filter or a flow-sensor fault. You can observe the external switch and DB breaker, but do not open the heater or reset internal cutouts yourself.
- Should I keep pressing the reset button on my water heater?
- No. An ELCB and a thermal cutout protect against different faults, and many storage-heater thermal resets sit inside the cover. Use only an external user control exactly as the model manual instructs. If it trips again—or there is heat, smell, tingling or moisture—leave the heater off and arrange a qualified check.
- Why does my storage water heater take so long to heat up?
- Possible causes include a failing or fouled element, thermostat or control fault, supply-voltage issue, mixing-valve problem, or a demand that exceeds the tank's rated recovery. Mineral deposits can contribute, but Singapore water hardness varies and is not a diagnosis by itself.
- When should I replace my water heater instead of repairing it?
- Replace a storage unit when the tank itself is confirmed perforated, or an instant unit when its sealed heating chamber is cracked and the manufacturer does not support a safe repair. For other faults, compare diagnosis, parts availability, warranty and compliant replacement cost; age alone does not decide it.