Well Steve, you have obviously done your research, as you can gather from this site the general opinion is for unvented magaflow type of system,
That is because of gross ignorance. It doesn't inspire confidence does it!!! No engineering knowledge whatsoever in most of them. A bunch of bathroom changers.
excluding drivel who clearly likes therma store. We (the general population) are either all stupid, narrow minded or talking with a degree of experience and knowledge.
Not the latter that is clear. An unvented cylinder is just a cylinder full of hot water at mains pressure, that is a potential bomb - that's all.
Heat-Banks
Instant high pressure hot water - When the thermal-store has reached the set temperature, water is delivered instantly at the taps.
Usable hot water in a matter of minutes - From a heatup from cold usable hot water is available at the taps within minutes.
Radiators hot in few minutes - On CH switch on, the pre-heated stored water is pumped into the radiators within a few minutes giving instant heat up.
Very high water flow-rate - The high-end heat-banks have a flow-rate up to 45 litres/min.
Operates on low incoming pressures - Requires a supply pressure of 1 bar to obtain a good flow-rate.
Operates on high incoming pressures - Will operate up to 10 bar without a pressure reducer.
Long efficient boiler burn - Reduces boiler on-off cycling increasing efficiency. Inefficient boiler cycling is no longer a major problem with boilers with forced flues.
Maintains optimum boiler temperature range - The boiler Deta T is maintained giving boiler high efficiency and longevity.
Combines the output of the stored water and the boiler -
Cylinder may be smaller for a similar performance
Cylinder at low pressure - Unlike an unvented cylinder it does not store water at high pressures. No risk of an explosion.
Fast cylinder recovery rate - When the boiler is connected directly to the heat-bank or an indirect coil, the recovery rate is rapid.
Legionella bacteria eliminated - The Legionella bacteria cannot survive in the high temperature sealed conditions of a heat-bank's DHW section.
No scale build-up in heat-bank - Containing primary and not secondary fresh water, scale does not build-up inside the heat-bank, either on primary coils or immersion heaters.
Cold water storage eliminated - No need for cold water storage tanks.
Solar heating storage - Water heated via solar panels may be stored in the heat-bank via a solar coil.
Caters easily for multiple heat sources - Electric, gas, oil, solar, solid fuel and heat pumps can safely heat the one cylinder. The ideal solution.
Easy maintenance - If an external plate heat exchanger requires cleaning or replacing it is a matter of draining down the heat-bank, or closing isolating vales, and unscrewing the plate heat-exchanger. In some rare instances plate heat-exchangers are fitted directly inside the heat-bank preventing the unscrewing of the plate, however, de-scaling can be performed.
Easy to improve hot water flowrates - By simply adding additional plate heat-exchangers in parallel, hot water flow rates may be improved. Retrofit additions are possible if extra bathrooms or showers are installed.
Stored water vessel need not be cylindrical - As no internal coil is used for hot water heat transfer the stored water vessel may be any shape, as opposed to a thermal store which has to be cylindrical for maximum efficiency. Unvented cylinders need to be cylindrical to create a robust shape because of high pressures. This shape advantage is ideal where space is limited, promoting excellent packaging.
Integrated Heat Banks can run CH off cylinder - This enables TRVs on all rads when using an auto speed pump like a Wilo Smart or Grundfos Alpha. This give instant heat up in the mornings.
Creates a Superb CH buffer for free - A CH buffer is created, evening out heating distribution to demand. This puts less stress on the boiler.
Boiler sized for average not peak use - This means a cheaper smaller boiler may be used.
Boiler can be a simple and more reliable - Boiler need not have complex modulating controls. A simple none-modulating boiler may be used.
Boiler can be large and not cycle, giving fast recovery rates - Boilers can be large and be accommodated and not cycle as overlarge boilers do when connected directly to radiators. The heat up recovery rate is very fast.
Failsafe - When open vented, the system is failsafe and cannot explode.
No Overflow Pipes - On some models a discharge or overflow pipe is unnecessary. This means a heat bank can be fitted centrally in a house and not near an outside wall
Full DHW & CH Electric Backup - Electric immersions can provide CH & DHW backup.
Unvented cylinders
Air pocket reinstatement - On some models, not all, the air pocket cushion at the top of the cylinder needs to be reinstated approximately once a year.
Certified installation - Installation in the United Kingdom are to be performed only by a heating engineer or plumber who is certified to fit unvented cylinders.
Regular Annual service checks - Unvented cylinder models require periodic service checks by a certified installer. A cost just to store hot water.
Sacrificial anode replacement - If fitted, needs replacing approximately every five years.
High-pressure relief valve and pipe - A large bore pipe leading to outside of the house needs to be installed.
Loses heat - Heat is lost from the stored water in the cylinder when standing over a period of time.
No secondary back-up of water - If the mains supply fails, there is no cold water storage.
Three port mid-position valves unsuitable - On the primary heating circuit, only motorised zone vales incorporating a spring return to close when the motor is de-energised can be used. It is possible for a three port mid-position valve to fail on open raising the cylinder temperature.
Cannot run CH off the cylinder
Not failsafe - Can explode if safety devices fail.
Also look at for further info:
http://www.heatweb.com/products/cylinders/heatbank/pandora.html
