Is it normal for my hot water system to drip from the valve?

Every storage hot water system has a temperature and pressure relief valve, usually near the top of the tank, with a drain pipe running down towards the ground. It opens if the pressure or temperature inside the tank gets too high. On many systems it also lets out a small amount of water during each heating cycle as the water expands. Some systems have another valve on the cold water side that does a similar job.

Never block, cap or tie off the valve or its drain. It's the safety device that stops pressure building up inside the tank.

A valve that drips constantly, even when the tank isn't heating, is usually worn or has grit in its seat. A heavy, steady flow can mean the mains pressure is too high or the pressure limiting valve has failed. Either way you're wasting water and, with an electric or heat pump system, paying to heat water that goes down the drain.

Very hot water or steam from the drain is more serious. It suggests the water is overheating, often because a thermostat has failed on an electric tank. Keep clear of the drain and switch the hot water circuit off at the switchboard if it's safe to reach.

Valves, water pressure and the tank's water side are work for a licensed plumber. The thermostat, element and circuit on an electric or heat pump unit are electrical work, which our team tests. If the tank is older and the valve keeps playing up, weigh a repair against replacing the system on your own timing rather than after it fails.