If your water heater isn't heating the water, you're not alone: it's one of the most common household problems. You step into the shower and the water comes out cold, or hot for a moment and then freezing cold, or it simply doesn't work at all. The good news is that in most cases it's easy and inexpensive to fix if you can identify the cause. Here we review the 8 most common causes, from most frequent to least frequent, so you know where to start.
First of all: rule out the obvious
Before assuming there's a malfunction, check three things that cause more "it's broken" calls than you might think: that the gas valve is fully open, that there's sufficient water pressure (turn on a tap and check), and if your model uses batteries for ignition, that they aren't dead. Once you've checked these, if the problem persists, keep reading.
1. No hot water comes out at all, the flame never ignites
This is the most common problem of all. The culprit is almost always the microswitch, the part that detects when water has started flowing and signals the flame to ignite. With use, it wears out and loses contact. It's an inexpensive part and relatively easy to replace.
If the microswitch is working, the next suspect is the gas solenoid valve, which can get stuck and not allow gas to pass through even if the rest of the system is working.
2. The water comes out hot and suddenly cools down abruptly
This pattern usually points to the turbine hydrogenerator, the component that generates the electricity needed to keep the flame lit while water is flowing. If it starts to fail, the heater "loses the signal" that water is still circulating and shuts off the flame abruptly, even though water continues to flow.
3. The water never gets fully heated; it always comes out lukewarm
The usual suspect here is limescale buildup inside the water heater, especially if you live in a hard water area. Limescale reduces the flow of water through the heat exchanger and limits how much it can heat up. It could also be the temperature limiter, which cuts off the flame prematurely for safety if it (erroneously) detects overheating.
4. It turns on and off by itself; the flame goes out after a few seconds
It's almost always the thermocouple or the draft control device (which monitors that the flue gases are escaping correctly). These are safety components: if they detect any anomaly, they automatically shut off the gas to prevent risks. Over time, they get dirty or worn out and start malfunctioning for no apparent reason.
5. It makes a strange noise or a bang when turned on
A small "poof" or sharp knock when lighting the gas stove is usually due to a dirty or improperly adjusted burner, and in some cases, the gas valve itself. It's not cause for immediate alarm, but it shouldn't be ignored for too long: if the problem is with combustion, it can end up damaging other parts.
6. It's leaking water, there's dripping or moisture around it
The first step is to pinpoint exactly where the water is leaking from. If it's coming from the inlet or outlet connections, it's almost always a O-ring , a very inexpensive repair. If the leak is coming from the heater body itself (a crack), unfortunately, it usually requires replacing the entire water heater unit.
7. The pilot light does not turn on even when I "click" the remote control
Check the piezoelectric igniter or spark plug. It's the part that generates the spark, and it loses power over time. If you see a spark but the engine doesn't ignite, it's more likely due to dirt in the pilot burner than a problem with the ignition itself.
8. It smells like gas
This is not a DIY project. If you smell gas near the water heater, turn off the gas supply, ventilate the room, don't turn on any lights or use any electrical appliances in the area, and call a certified technician immediately. None of the above problems should produce a gas smell; if they do, it's a sign of a leak and must be treated as an emergency, not a weekend fix.
Repair it yourself or call a technician?
Repairs to parts 1, 2, 3, 6, and 7 are generally manageable for someone with basic DIY skills and tools, and the parts are readily available so you don't have to replace the entire water heater. However, issues related to the draft control, thermocouple, or any indication of a gas leak (points 4 and 8) are best left to a qualified technician, as they directly affect the appliance's safety.
If you're unsure which part you need for your exact model, you can locate it by reference in our spare parts finder , or write to us and we'll help you identify it.
