"Harry Ziman" hziman at clara dot co dot uk wrote in message
...

We have an old farmhouse with the hot water/heating system confidgured as
follows.

Boiler 1: 110,000 BTU 16 radiators in the "front" of the house

Boiler 2: 110,000 BTU 6 radiators, hot water in the "back" of the house

Aga: Hot water in the front of the house

In case you are wondering the house was once divided into two each with
its
own heating and hot water system - they are independent with their own
header tank, timer, pump, hot water tank.

Needless to say this is not very convenient - to heat one of the bedrooms
we
need to put the second boiler on. The two boilers sit next to each other
in
the boiler room so we would like to combine the systems. The question I
would like to ask is how to organise the boilers. Do they go in series
(i.e.
water through one then the other)

No.

or parallel (i.e. split the water flow so
it can run through either boiler and then recombine).

Yes.


CanI safely run one
boiler and when I need the extra heat switch the second one on?

Yes.

One person
has todl us that the boilers must go in series and both be controlled
identically - same temperature and same time-controls.

Not so.

Have a vertical 32mm header pipe. At the top have an automatic air vent.
Just below each boiler tees in its 28mm flow pipe. The same at the bottom
of the header pipe for the boiler return pipes. Each boiler has a pump on
its own 28mm flow pipe. In the centre have the flow and return to the DHW
and CH, with both tees as close as possible.

Is your mains pressure good? If so install a direct heat bank and eliminate
the existing cylinder(s) and cold water storage tanks and have full mains
pressure. A heat bank will also work with DHW fed from a cold water storage
tank too. The heat bank creates a neutral point for all heat apliances to
connect and also the CH circuit. Have 3 flow tappings and three return
tappings on the heat bank. Each boiler, each with a pump, and the aga
connect to the heat bank cylinder. Take the CH flow and return off the
bottom of the heat bank using a pump in either the flow or return. The DHW
will be taken off the heat bank too. If the heat bank is sized up right you
will not need a radiator to dissipate heat in summer from the aga.

See:
http://www.heatweb.com. Look at the examples of customer systems.

Before anyone asks, I know that the header tanks need sorting out so there
is only one. Also, I do not want to go to the expense of a new boiler with
the capacity for the whole house.

We would also like to rationalise the hot water system so the Aga heats
water for the whole house. This is a little more involved. Can I direct
the
flow through two separate hot water tanks? If not, how about a valve and a
timer to regularly switch alternate from one to another. Failing that I
guess I will need to remove one of the tanks and accept that it will take
a
long time for hot water to flow to some parts of the house.

I doubt the Aga will cope heating two hot water cylinders.

Do let me know if any of this fails to make sense and I will try to
explain
further.

Thanks

Harry