Most manufacturers recommend that unvented water heaters are serviced each year is to ensure that safety valves are tested for faults. The role of the safety valve is to guard against systems overheating, becoming over pressured and causing floods. Whether you have noticed that a safety valve has malfunctioned or whether it was identified as faulty in a service, it should only be changed by a competent person.

What Is a Safety Valve?

Unvented hot water cylinders are under a good deal of pressure. This allows them to supply hot water to the tap at a rate that matches or exceeds mains pressure, which is the maximum a vented hot water heater can supply.

However, there are potential dangers with unvented cylinders. One of those is the potential to become over-pressurised. If this occurs, there must be a way to eliminate the excess pressure to avoid catastrophic failure of the cylinder wall or other components. The safety valve is responsible for releasing this pressure in these instances.

There is also the potential for water within an unvented cylinder to become overheated. In normal operation, a thermostat controls the heat of the water, allowing the immersion heater to achieve the right temperature and then stopping the increase before it becomes too hot. However, if the thermostat were to fail, then there is the potential for the water to become overheated. In this instance, a similar situation to over-pressure could occur, creating a dangerous condition. The safety valve is designed to release water if it exceeds a specific temperature.

As you can see, the safety valve within an unvented cylinder is a critical component. It ties in directly to the safe usage of the system. Under normal conditions, it should work correctly for years, but there are potential issues that could render your safety valve unable to function properly.

Why Would a Safety Valve Fail?

A safety valve can fail for a number of reasons, but the most common is deterioration of the washers, gaskets, and other rubber components. This is often due to prolonged exposure to high temperatures as well as a lack of adequate maintenance during annual inspections. The point of the mandatory annual inspection for unvented hot water cylinders is to ensure safe operation of this critical component and timely replacement in the case of deterioration.

The first set of photographs show a temperature and pressure relief valve being changed. The valve on an Albion Stainless HE unvented water heater began allowing water to be discharged from the cylinder at 50°C instead of the 90 – 95°C. As a result water was discharged under normal conditions causing a waste of water and electricity.

These photos show the steps an EasyFlow heating engineer would take to replace the valve. As is the case with immersion heater replacement the electrical supply should be isolated and the cylinder drained down.

We cannot stress enough that replacement of any components on an unvented hot water heater be handled by trained, certified, and experienced professionals. At EasyFlow, our service representatives have years of experience with repairs, part replacement, and new installation on vented and unvented thermal stores, and they can provide you with an expedient, professional solution to your needs, whether the TPR valve has failed, the combination valve is at fault, the immersion heater has stopped working, or something else has gone wrong with your water heater.

The combination valve is a combination of a line strainer, single check valve and a pressure reduction valve. Often and in the case of the combination valve on the MegaFlo water heater shown in the photos it is also connected to an expansion valve.