Common problems with hot water heaters

Whether you are installing a hot water heater in a new home or replacing an old one, it's useful to know what common problems different types of water heaters are prone to. Of course you must realize that different types of water heaters – and even specific models – may have different tendencies. But here we are looking at generic problems that you might come up against with gas, electric, tankless and solar water heaters in general. These include a failure for the heater to get hot; leaks; and odd sounds and smells.

Water fails to get hot enough

When a gas hot water heater is not making your water hot (or simply not hot enough) it is often related to the supply of gas to the heater, but could also be because the thermostat is faulty. If your have a gas hot water heater, turn the control knob to "pilot" and then check to see if the gas is in fact switched on. It should be obvious that if the pilot light is burning, the gas IS on. If it isn't burning, and the gas is on, relight the gas, making sure that the gas inlet valve is open. If you've followed the correct procedure and the pilot still will not light, there's a possibility that the thermocouple is faulty – which will mean calling in a professional to do a repair.

If the pilot light won't stay on, and the thermocouple is sound, it could be that the orifice has become dirty and clogged. Another cause could be that the gas control valve is faulty, or that the gas pressure is too low.

The thermostat should not be set higher than about 120 °F or 50 °C. If it's set a lot lower than this you might find that the hot water is not warm enough, particularly if you are showering and want to mix hot and cold water together. If the thermostat is set at the optimum temperature for your needs, and you still don't get a suitable result (in terms of heat), it is important to have the thermostat checked by a plumber.

If yours is an electric hot water heater, and it is not heating the water adequately or at all, there could be a problem with the heating elements or even with the control switches or buttons. But first check that power is being delivered to the unit. If the power trips, a fuse may have blown. This is a simple problem to fix, but if it recurs, you'll do well to call in an electrician to check the problem.

Most other problems should be checked by a qualified plumber. For instance if there is water inside the cylinder, the thermostat may be malfunctioning, although if this is the case, you're probably going to have to buy a new water heater.

Water is too hot

While you can generally control the water temperature with the thermostat, malfunctioning hot water heaters sometimes deliver water that is much hotter than it should be. You may even hear boiling-type sounds inside the heater. Clearly this is because the appliance is not shutting off at the temperature that has been set. Generally this is more of a problem with pressure hot water heaters, and often because the temperature-pressure (TP) or pressure releasing valve is faulty.

Since people can be scalded by hot water or steam, it is best to immediately call in a plumber or someone recommended by the water heater manufacturer. Untrained people should not be permitted to replace this type of valve.

Hot water heater is noisy

It can be very disconcerting when a water heater makes peculiar noises, even if the cause is simply the result of metal expanding and contracting.

If you here odd sounds coming from your geyser or tank, it's wise to find out the cause. Often sediment – which might be dirt, scale or minerals from the water – builds up inside the cylinder and causes a rumbling, gurgling or popping noise. While this isn't dangerous as such, sediment can eventually get so bad that it affects the efficiency of the heater. Eventually it could cause the unit to fail completely.

You can minimize sediment build-up by regularly draining and flushing your hot water cylinder.

If you hear what sounds like water boiling inside the cylinder, call in a professional. This is not the sound that sediment produces.

Smell coming from hot water cylinder

Water that flows out of a hot water cylinder should never smell bad. If the cold water also smells, it could be the water source, in which case you will need to call your water supply company – unless of course you are drawing water from a borehole. If it is just the hot water that smells, and you have a gas heater, chances are it is leaking gas that is causing the smell. Shut off the pilot light and close off the gas at the valve, and call in an expert to assess the situation.

Another common cause is that the heater's anode rod and the water (which has a high concentration of sulfate) are reacting to one another. If replacing the anode doesn't do the trick, you're going to have to call in a plumber.

To be sure that it is the hot water heater causing the problem, you need to check that the same smell occurs at all the taps and other outlets. Other reasons for smells that seem to come from the cylinder include bacteria in the sink overflow, polluted drain, sewer or vent systems, and even a faulty trap in the system that is accumulating muck that is rotting and smelling bad.