Megaflo FAQ

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A Megaflo or Unvented System provides high pressure hot water. The hot water flow rates are very much better than traditional open vented systems which rely on gravity and the height of the water tank. Additionally, all cold water outlets are supplied directly from the mains, giving high pressure fresh water throughout the property. As a rough guide, the hot and cold water outlets on an unvented system, will operate at a pressure similar to the outdoor garden tap! Megaflo are the market leading brand of domestic unvented cylinders. For more information see our section on Megaflo Systems.
Inlet pressures typically range from 1.5 bar to 3.5 bar. A pressure control valve is used to ensure the maximum pressure is not exceeded.
Unvented hot water systems should only be installed and serviced by a qualified and competent person holding a current G3 Unvented Qualification. It is extremely important that the system is installed correctly, together with all essential safety controls. Building Regulations require installations of unvented hot water cylinders to be notified to the local Building Control. If the installer is a member of a Competent Persons Scheme, they will take care of this, and the customer will receive a Building Regulation Compliance certificate.

Ideally, the mains water pressure at peak times should be a minimum of 1.5 bar dynamic pressure, although all unvented systems will operate at pressures as low as 1 bar dynamic pressure. The size of the incoming main ideally needs to be at least 25mm MDPE or 22mm copper, in order to provide adequate flow. Megaflo Unvented will check and assess these parameters as part of our free on-site survey. For properties with multiple bathrooms, a higher flow rate would be required to meet the required demand.

Where the mains water supply is not suitable, then Water Boosting may be required.

As an Unvented cylinder is pressurised, it can be installed in almost any location. This can be a loft, garage, upstairs, downstairs or even in a basement. The cylinder requires installation of a safety discharge pipe, and in some basement locations, a sump and pump may be required. This is will be determined at the site survey, and advised as necessary.
Several safety controls are in place to protect the householder (or users) and property. They ensure the water temperature never exceeds 90-95°C and the pressure remains within safe limits. These controls are NOT optional: they are absolutely essential and they must be kept in good working order. They typically comprise the following:- Control thermostat which is typically set at between 60 and 65°C. High level, energy cut out device with manual re-set, usually set between 85 and 89°C. Temperature and Pressure Relief Valve set to 90 – 95°C or 10 bar pressure. Expansion relief valve set to 8 bar pressure. Additionally, the two electrical thermostats (control and high level) and wired into a motorised valve such that any indirect heat source will be closed-off and fail-safe
Yes, most unvented cylinder manufacturers specify an annual service, which is also required to maintain their manufacturers warranty/guarantee. This typically involves cleaning filters, checking and testing the safety components, valves and thermostats. We also check the thermostat wiring and general performance of the overall system to ensure everything is working as designed. As we specialise in this field, we can quickly identify issues or potential problems.

All unvented hot water systems should have a tundish fitted. This provides an air-gap in the discharge pipe and also enables any discharge from the safety devices to be seen, as it runs through the pipe. The required installation and positioning of the Tundish is controlled and documented in the Building Regulation G3 Approved Documents.

Dripping water in the tundish may indicate a problem with the hot water system. It may a safety device, the expansion vessel (or air bubble), or the pressure reducing valve. Additionally, if a sealed heating system is plumbed into the same tundish, it may indicate a problem with the heating system. It would be advisable to have a qualified Unvented Engineer diagnose and rectify the problem.
In a Megaflo or Unvented system, this may be an installation/design fault or faulty check valve. If the cold water runs warm for a short period of time, before returning to a normal cold supply. This is more of an inconvenience than a major problem, but generally straightforward to rectify! In some cases with earlier versions of the Megaflo cylinders, this happens when the system has been installed with a balanced cold supply. This may be more noticeable after the air bubble has been recharged following a routine service. Sometimes the warm water may be the result of heat transfer from hot pipes in close proximity to cold pipes. In traditional vented (or gravity) systems, this situation may indicate a more serious and potentially dangerous problem. If the cold tap continues to run with hot water, we would recommend switching off the hot water and having it checked as soon as possible. If the hot water is circulating with the cold water storage cisten (in the loft) or if water is boiling in the cylinder, then immediate attention should be sought.
Every Megaflo installation is different and costs vary according to many different factors. Two significant considerations are the size and location of the mains water pipe within the house, and also the proximity of the Megaflo Cylinder to a safety discharge outlet (e.g. an external wall). Electric (Direct) systems are generally cheaper to install, as they are not linked to a heating system. It is vitally important that any unvented system is correctly installed. There are numerous unethical ways of cutting costs, but for safety and moral reasons, we as a company will never engage that route. We make no apologies for being at the upper end of the price band, as all our customers benefit from our expertise and exceptional levels of service! Megaflo Unvented always carry out a full on-site survey, and our quotations allow for a professionally installed system designed for optimum performance.

Unvented systems require sufficient incoming pressure and flow to be able to service all outlets within a property. If there is insufficient flow, then an accumulator may offer a suitable solution. An accumulator is a vessel that stores water under pressure and is typically installed on the incoming mains supply to provide a buffer store of pressurised water. This offers a simple and effective solution to address flow rate issues found in properties with multiple bathrooms.

The Megaflo cylinder is designed with an internal air bubble, to absorb the expansion as the water is heated. Other brands of unvented cylinders may use an external expansion vessel to provide the same function. This is also mentioned above in What is the expansion vessel for?
Over time the Megaflo air bubble may be absorbed into the water, in which case the air bubble will need replenishing. This is done as part of the annual service, but any competent person can reinstate the air bubble by following the instructions on the side of the cylinder. If in any doubt, please refer to a G3 qualified engineer.

As the mains water is heated under pressure, tiny bubbles are absorbed into the water. As water is drawn off at the outlet, the water returns to normal atmospheric pressure and the bubbles are released, giving the appearance of cloudy water. This is completely harmless and normal. It may be more noticeable in the winter months when the incoming water is cooler. As long as it clears without leaving any sediment, there is nothing to worry about.
In this context, it refers to the hot and cold water supplies. Generally, showers and mixer taps are designed for balanced supplies where the hot and cold water are at the same pressure. Where possible, we generally recommend installing balanced supplies to bathrooms and mixer taps. In areas with high water pressure, say greater than 3 bar, it is even more important to consider having balanced hot and cold supplies otherwise the cold water (unregulated) pressure may overcome the hot water pressure, which is typically reduced to 3 bar by the Megaflo pressure reducing valve.
If the hot water pressure has deteriorated over a period of time, there are a number of potential causes. It may be the inlet filter is blocked, or with older systems, the PRV (Pressure Reducing Valve) cartridge may have failed such that it restricts the flow. The problem may be more noticeable with higher outlets; for instance, a shower in the loft may suffer more than a shower on the ground floor or basement.
For properties with long pipe runs or large bore pipe work (or both!) from the cylinder to the outlets, it’s quite likely there will be a significant delay in getting the hot water. The volume of water in the pipe work needs to be drawn off before the warm water gets through from the cylinder. In this scenario a Secondary Circulation loop addresses the issue by circulating hot water in a closed loop to run in close proximity to each outlet. This can usually be fitted retrospectively, but can be quite disruptive depeding on access to pipe and pipe routing. See our page on Secondary Circulation which includes a more detailed explanation with diagram.

Why Choose Us

At Megaflo Unvented, we do what we say we’ll do. Our integrity and competence values demand this. We are accountable for our words and actions, and that we deliver a service that meets or exceeds all expectations of quality and timeliness.

Customer service is our highest priority and to reinforce this, we adhere to the following guidelines:

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