Why Is There a Drip through the Tundish on my Unvented Water Cylinder?

Unvented hot water cylinders offer many benefits over old-style vented systems. They offer full mains pressure at every tap, good flow in showers throughout the home, regardless of elevation or distance from the water heater, and more. They’re efficient, well-insulated, and cost less to operate, and they are also easy to maintain.

However, for all those benefits, they are pressurised systems. When water is heated, it expands, putting pressure on the insides of the cylinder walls and other components. If left unchecked, that pressure could eventually lead to catastrophic failure.

Safeguards are put in place to prevent that from happening. One of those safeguards is the pressure relief valve – the name is self-explanatory. This valve opens if the system’s pressure rises too high, allowing excess pressure to be vented into the airing cabinet around the cylinder.

However, pressure relief valves can and do fail. In this case, water will drip through the tundish. Another possible cause of water dripping through the tundish is if the pressure inside the cylinder is rising too quickly.

If the pressure relief valve fails, it will allow water to flow out through the valve and then through the tundish to the drainpipe. You may also notice a drop in system pressure – if the valve fails and is leaking, then the system will not be able to generate the correct amount of pressure. However, seemingly normal pressure at the taps does not guarantee that your pressure relief valve has not failed.

Another cause of water dripping through the tundish is if the system has become over-pressurised and the relief valve has opened. In this case, the valve opens, excess pressure is released, and water flows from the valve, down the pipe, through the tundish, and then out the drainpipe.

It’s important to understand two things: First, this is precisely how the pressure relief valve is designed to operate. Second, the symptoms are identical to those of a failed pressure relief valve, so the only way to determine the actual problem is to have a G3-certified plumber inspect the system.

Whether due to a faulty pressure relief valve or an over-pressure situation, chances are good that the problem could have been avoided through simple maintenance. While unvented water cylinders do not require extensive maintenance, they do require an annual inspection for potential problems, as well as important testing and cleaning. The pressure relief valve should be tested annually – if it is showing signs of wear and tear or other forms of degradation, a G3-certified plumber can replace it immediately, avoiding the problem of spotting water dripping through the tundish and emergency repairs down the road.

Have you noticed water flowing through the tundish? It could be one of two problems, but the solution for both is the same: Contact EasyFlow today to schedule an inspection and repair. We carry replacement parts for most unvented water cylinders in our vans, ensuring swift, professional repairs.

We cover the areas of Greater Manchester, Liverpool, Chester and Leeds. Call us on 0161 941 5571