As a DIY newcomer I have been reading up about plumbing systems with a view
to trying to understand my own plumbing system, but I don't seem to be quite
able to get to the bottom of it....

My 2-storey house has no loft, storage tanks, hot water cylinders or airing
cupboards of any kind. All the hardware is in the garage, which is separated
from the house by a 1 metre-wide path. In the garage there is a Potterton
Netaheat Profile boiler, and a Megaflo unvented HW storage unit. So I have
an unvented mains-pressure system, which explains why all the H and C taps
throughout the house are so powerful - nice!

At the top of the garage rafters there is a small, well-lagged water tank.
The top and bottom of the tank are connected by a pipe loop, and a branch
from this loop feeds the boiler's "flow pipe", which in through another
branch feeds the HW tank (this bit seems clear). Another pipe, this one
well-lagged, from about the middle of the tank seems to disappear under the
ground towards the house.

Things I would like to know:

- I don't quite understand why I need the tank - purely because the boiler
isn't designed to be fed mains-pressure water? All the "unvented systems"
diagrams I have read up on omit tanks of any description.
- Why is the tank so well-lagged? Doesn't all HW go to the Megaflo?
- Clearly the Megaflo feeds the H taps and showers in the house - presumably
it also feeds the radiators? Or might that be the job of the lagged pipe
from the lagged tank in the garage roof that seems to go under the ground
towards the house?

Sorry if this is so basic!

Thanks for any advice.

Richard Clay wrote:

As a DIY newcomer I have been reading up about plumbing systems with a view
to trying to understand my own plumbing system, but I don't seem to be quite
able to get to the bottom of it....

My 2-storey house has no loft, storage tanks, hot water cylinders or airing
cupboards of any kind. All the hardware is in the garage, which is separated
from the house by a 1 metre-wide path. In the garage there is a Potterton
Netaheat Profile boiler, and a Megaflo unvented HW storage unit. So I have
an unvented mains-pressure system, which explains why all the H and C taps
throughout the house are so powerful - nice!

At the top of the garage rafters there is a small, well-lagged water tank.
The top and bottom of the tank are connected by a pipe loop, and a branch
from this loop feeds the boiler's "flow pipe", which in through another
branch feeds the HW tank (this bit seems clear). Another pipe, this one
well-lagged, from about the middle of the tank seems to disappear under the
ground towards the house.

Things I would like to know:

- I don't quite understand why I need the tank - purely because the boiler
isn't designed to be fed mains-pressure water? All the "unvented systems"
diagrams I have read up on omit tanks of any description.

Clearly you have not seen diagrams for the correct layout of an unvented
HWC as opposed to boilers with unvented primaries.


- Why is the tank so well-lagged?
Against frost.

Doesn't all HW go to the Megaflo?
No presumably the boiler also heats the radiators.

- Clearly the Megaflo feeds the H taps and showers in the house - presumably
it also feeds the radiators?
No the boilr will do that.

Or might that be the job of the lagged pipe
from the lagged tank in the garage roof that seems to go under the ground
towards the house?
Almost certianly.

OK High tank in garage is the header tank to the boiler and rads. It
will be just(?) higher than than the highest rads in the house?

IIRC the connection to the Megaflow that is about 1/3-1/2 the way down
will be the releif valve.

There are five holes on the Megaflow 3 connect to the HW in the
cylinder, the other 2 are the coil connections to heat the water in the
cylinder and connect to the boiler.
The top is the HW outlet, the bottom one is the CW inlet and the other
the releif outlet.

HTH






---
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

- I don't quite understand why I need the tank - purely because the
boiler
isn't designed to be fed mains-pressure water? All the "unvented
systems"
diagrams I have read up on omit tanks of any description.

Clearly you have not seen diagrams for the correct layout of an unvented
HWC as opposed to boilers with unvented primaries.

Thanks for your advice. Could you just clarify the bit above please? What
exactly is the difference between the 2 setups you mention? What's a
"primary" in this context? (I assume "HWC" is "HW container"?)

Thanks again
Richard

Richard Clay wrote:

- I don't quite understand why I need the tank - purely because the
boiler
isn't designed to be fed mains-pressure water? All the "unvented
systems"
diagrams I have read up on omit tanks of any description.

Clearly you have not seen diagrams for the correct layout of an unvented
HWC as opposed to boilers with unvented primaries.

The HWC (HW cylinder) is unvented, that is there is no way for the water
to leave the cylinder except via the taps (or when there is a problem
via the releif valve). This contrasts with the normal HWC often found in
a first floor airing cupboard where the top connection leads to a vent
pipe which goes up into the loft higher than the cold water tank. Were
the water in a vented cylinder to boil (which can happen if an immersion
heater fails) then water/steam escapes via the vent pipe.

The water in the boiler and rads is sperate from the HW used a the hot
taps. This water and its circuit is known as the primary. This water
comes form a small open header tank (vented) or is sealed (unvented) see
the FAQ below. You have a vented primary circuit fed from the small well
lagged tank.


Thanks for your advice. Could you just clarify the bit above please? What
exactly is the difference between the 2 setups you mention? What's a
"primary" in this context? (I assume "HWC" is "HW container"?)



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html