How to Prevent Unvented Cylinders from Leaking and Faults

The issue of leaking or underperforming unvented cylinders is not something we are faced with on a regular basis, especially as our primary products are copper cylinder which are proven to be more durable than stainless steel cylinders and less susceptible to corrosion.

However, on the very rare occasion, a client does experience a problem, the cause can generally be pinned down to one common factor – the cylinder not being serviced annually.

As a pressurized unit, the performance of the connections, pressurized valves and expansion vessel will play a major role in preventing issues occurring.

The potential faults which can occur if the annual service is not carried out on an unvented cylinder include:

  1. Issue with Expansion Vessel

The expansion vessel contains a neoprene diaphragm surrounded by an inert gas which is charged to match the pressure entering the cylinder. As the water in the cylinder increases in temperature, the additional water volume is accommodated by the expansion vessel.

If the charge in the vessel is too low, additional pressure is put on the cylinder which overtime can reduce its lifespan.

As part of the annual service, the pressure in the vessel should be tested and recharged when required. Where the charge is lower than normal, the vessel would be tested to identify any small punctures in the diaphragm before it becomes a major issue.

We are now supplying nitrogen filled expansions vessels with all unvented cylinders which hold their pre-charge for longer.

  1. Issue with Pressure Reducing Valve

The pressure reducing valve limits the mains pressure water entering the cylinder and allows the entire water system to be balanced. It also protects the cylinder and keeps it working to its designed pressure.

As part of the annual service, this valve is tested to ensure it is operating properly and within safe levels. The internal filter is removed to check for any debris which could affect the pressure of the water.

  1. Issue with Expansion Valve

The expansion valve is another safety feature which is designed to release pressure in the cylinder should it get too high.

If the valve is not operating properly then it could cause major issues for the cylinder. If its set too low, the cylinder is likely to be discharging water on a regular basis and as a result wasting energy and therefore cost.

If its set too high, the pressure within the cylinder can rise to dangerous levels and potentially result in leakages.

The annual service would test to ensure the expansion is operating within the correct parameters and replaced if necessary.

  1. Issue with Temperature and Pressure Relief Valve

The temperature and pressure relief valve is primarily a back-up safety valve which reacts to the temperature (and therefore impacts on the pressure of the cylinder) and will only activate should the expansion valve fail.

This valve contains a wax rod which melts when the water reaches a certain temperature, normally 90 degrees centigrade, and discharges the water to release the pressure.Should this situation arise and the wax rod melts, the temperature and pressure relief valve must be replaced.

The Annual Service will ensure this valve is not damaged and is in good condition.

  1. Faults with The Thermostat

Most unvented cylinders will feature a thermostat which controls the heat transfer process within the cylinder and prevents overheating, which in turn will increase pressure on the system and result in high running costs.

Again, the annual service will ensure this is operating efficiently and providing adequate protection to the cylinder.

So whilst our POWERflow unvented cylinders are one of the most efficient and the most reliable on the market, it is vital the annual service programme is carried out by a qualified service engineers.

It’s also why we insist the service is carried out to ensure the warranty is maintained on the cylinder.


Click here to find out more on our POWERflow, ECOflow and STEELflow Unvented Cylinders or contact us now to discuss your project.

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