I was a doing Google and I caught this. My News server din't pick it up.
It requires attention.

Geosolar Heating )

At the risk of being associated with 'dumb
plumbers' I'll give my reasons for recommending
an unvented cylinder rather than a thermal
store. I've got nothing against the technology
of a thermal store but personally feel its had
its day now that condensing boilers will soon
be mandatory to the mass market.

Confusing passage but let's see....

I agree that an unvented cylinder must
be installed by a trained person. IMM
says that UV cyls can explode and while
true it is rare due to the safety features that
are mandatory. UK regulations are lot
stricter than many countries were UV cyls
have been the norm for many
years.

The point is that they can explode, and do. If one explodes an insurance
company will not pay out if the unvented cylinder was not serviced.

To the points in question;

1. Reinstating the air bubble in a megaflow
is not a difficult task.

It is for a pensioner. Many local authorities have removed unvented
cylinders as they had too much hassle of drips from vent pipes because the
air bubbles were never re-instated by the residents, or the pressure vessels
failed. They had an army of men attending these problems.

2. 1" copper overflows are not required
unless the route to discharge is extraordinarly
long. The tundish has a 22mm output and this is
sufficient for most installations. However, the
discharge pipework must not be plastic.

The large metal pipe extracts heat from a house 24/7. For this reason eco
houses don't us them. DPS do a heat banmk that doesn't require an overflow,
so no penetration of the external building fabric.

3. KISS. Which is easier to understand;
the UV cyl or a heatbank?

Both. If dumb plumbers can't understand a thermal store or heat bank they
should work on the milk.

4. Solar. As far as I know OSO and Viessmann
are the only UV cyls to have dual coil models.
Yes, the solar won't heat your radiators, but
since solar systems are designed to work at
their peak in summer, surely this a moot point?

It is not. Solar panels work in winter with clear strong sun. A solar coil
in an integrated thermal store supplying DHW & CH will have solar generated
heat used for CH and DHW. A solar coil in an unvented cylinder is only
available for DHW.

5. condensing boilers. I commented this
elsewhere in the NG. UV cyls are a better
option with a condensing boiler.

Clearly untrue. A heat bank with DHW and heating sections, with the heating
section controller from an outside weather compensator will perform very
efficiently with condensing boiler

With inefficient boilers there is no such choice
between an uv cyl and heatbank.

????

6. DIY. Yes I'll agree that a heatbank
can be DIY-ed. This suggests
the owner has some interest in the
heatbank technology, which is fair
enough.

Or wants high flow DHW cheaply as he can do it himself. It is not a matter
if he has fad for thermal store technology. A DIYer can't fit an unvented
cylinder.

Future owners may not be so inclined.

Future owners will not know the difference. All they know is that a heat
bank will give them high pressure DHW. Also a heat bank can go up to 10
bar, whereas I know of no unvented cylinder that is above 3.5 bar (they are
pressure (reduced).

Still, future employment
for 'plumbers' when the next owners
rip it out to put a megaflow in?

Ignorance from dumb plumbers. I know of one housing estate that were fitting
with Flowmaxes about 12 years ago . Some of the Flowmaxes developed simple
faults, such as flow blending valves failing and the likes. The naive
owners contacted the local dumb lumbers and said it is best to rip them out
and fit a tank in the loft. There are a number of tank now in lofts, when a
£30 part would have solved the problem.

I can give you examples of dumb plumbers putting in a rad system when a
perfectly adequate forced air system is there. All was required was the unit
repairing.

Most plumber are only good for drains and gutters and replacing bathroom
suites.

7. The marque. A 'Megaflow' has become
something of a must-have.
Probably due to marketing and keeping
up with the Jones.

Marketing has promoted an inferior technology that is clear. Also develoers
fitting them besuse they easy is also promoted them. Heat banks are just as
easy. Obviuosl a cheap was done somwhere. "Megaflows a must have" Please
get real.

Still, the educated customer wins out.
It may be a plus-point on a future house sale.

A megalflow or thermal store? When a customer sees high pressure mains hot
water he is impressed whether Megaflow or heat bank. Heat bank give higher
pressures, up to 10 bar.

8. Boiler cycling. Any system is susceptable
to this if badly installed. I've not seen a modern
UV cylinder which causes the boiler
to cycle before it reaches the desired temperature.

I have.

I only install the keston celsius 25, which has
some features to avoid cycling.

So you blinded by a boiler with load compensating control; the "only" type
you fit.

9. All in one packages. Not something I go
for myself but just a personal choice.

And no reason given. Not impressed.

There are equally valid pros/cons
for this type of unit.

You should be more objective when assessing these matters. You have
everything to gain.

Something tells me you want unvented cylinders to be the norm as only BBA
people can fit them. They are NOT cheap and BBA fitting not cheap either.
Your mind is poisoned by vested interest.