Unvented Hot Water Cylinder Problems & Cures

We have put together this Unvented Hot Water Cylinder Problems & Cures page to give you an idea of common issues and questions asked and what to do next.

General Fault Finding

Below we have compiled a list of potential faults that could occur in your Unvented Hot Water Cylinder

Faults with the Expansion Vessel

All Unvented cylinders require an Expansion Vessel to be fitted. The  cylinder heats the water and as a result, expands. This means it increases in volume.  The purpose of an expansion vessel is to take up this extra water so that it can’t escape from the sealed cylinder. The Vessel contains a diaphragm that is surrounded by a gas which is charged. This is where the additional water is forced into. If the charge is too low, the vessel will not accept the extra water and pressure will build in the cylinder which can reduce it’s lifespan and cause further issue.

Faults with the Pressure Reducing Valve

The Pressure Reducing Valve limits the mains pressure water that enters the cylinder. This in turn ensures that the system is balanced and keeps it working at the correct pressure level. A fault with this would mean full or reduced levels of mains pressure into the cylinder that drop below the recommended pressure for the system.

Faults with the Expansion Valve

The Expansion Valve is another safety feature. The purpose of which is too release some of the pressure in the cylinder to avoid any issues. If the cylinder is discharging water regularly, this may be because it is set too low. This would therefore be a waste of energy and cost. If it is set too high however, the pressure may reach a dangerous level. This could then result in potential leakages.

Faults with the Temperature & Pressure Relief Valve

The Temperature & Pressure Relief Valve is mainly a back up safety valve for if the Expansion Valve fails. The valve contains a wax rod that melts when it reaches a certain temperature in order to release the pressure. This may be faulty if it is opening at the normal operating temperature instead of a particularly high one.

Faults with the Tundish

The purpose of the Tundish is to highlight when water is passing through it which indicates a fault, potentially with one of the safety devices. If hot water is flowing through it may be an issue with the Temperature & Pressure Relief Valve. If cold water is flowing through it may be an issue with the Pressure Reducing Valve or the Expansion Relief Valve.

 Common Questions

  1. Why am I no longer getting any hot water?
    A common cause of a lack of hot water would be a faulty immersion heater. It may be that you need the whole heater replacing or it may be just a stat but an engineer will be able to confirm for you.
  2. Why am I getting no water all?
    A common cause of a complete lack of water could be the filter. It may have become blocked and will probably need looking at.
  3. My water is coming out way too hot, why is this?
    There could be a couple of reasons for this. Setting the stat set too high could be one reason. On the other hand, it may also mean that there is actually a problem with the stat. It may have become faulty. Replacing the stat would then be the only option.
  4. What should I do if I am not using my Unvented Hot Water Cylinder?
    Not using your boiler for a short period of time is absolutely fine. If it reaches roughly 40 or more days without being used though, it will have to be cleaned. This is because bacteria can build up. You will need to heat the boiler to kill the bacteria and allow it to go through one full cycle to get rid of the contaminated water.

Sales Service & Repair of Electric Thermal Stores.