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Complicated central Heating; Back-Boiler and Combi-Boiler



 
 
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  #1  
Old February 3rd 05, 01:16 PM
Junior Member
 
First recorded activity by DIYBanter: Feb 2005
Posts: 7
Default Complicated central Heating; Back-Boiler and Combi-Boiler

Hi,
Iím new here.
Iíve recently bought a house in Scotland as a holiday home.
At the present heating and hot water run of two back-boilers which are heated by open fires. (In two separate rooms)
There is a twin coil hot water tank in the drying room with gravity circulation. (I believe)
The central heating (9 radiators) is circulated by one pump. Both back boilers feed the central heating.
Can someone make an educated guess at how the water flow through the radiator has been designed?
Will it be kind of one circle with the water being pumped around and around?
If I remember rightly, the Radiator can be adjusted separately, so there must be some form of a bypass or something.

Sorry I canít give more precise information, but I live in Germany, and canít investigate into the system myself at the moment.

In May, I want to include a combination boiler into the system. Either gas or oil, I havenít decided on that point yet (no mains gas).
How do I best go about it?

I believe that I can get rid of the hot water tank under the roof, since Water will come directly from the new combi-boiler
Is it Ok to blank the gravity feed and return pipes from the boiler in the attic, or do I need to open the fireplace and blank the ends at the boiler? Or should I just short-circuit the pipes in the attic?

I would very much like to keep the back-boilers operational for heating purposes.
Is that possible?
I assume that the heating will be run of the combi-boiler a lot of the time. But when I light a fire I would like to have the feeling that Iím not wasting a lot of energy. So if it is possible I would like to have the back-boilers included into the system.
When the combi-boiler is heating the house, depending on the way the central heating piping has been designed; the back-boilers would act as a radiator warming the air in the fireplace and causing a drought up the chimney. ???
Would it be feasible to install a "Bypass" ??
Iím thinking of a 3 - way valve which sits in front of the water flow to the back-boiler.
In one position the water flows through the back-boiler and gets heated by the fire
In the other position the water flows through the bypass and doesnít heat the back-boiler unnecessarily.

Or am I construction a Bomb?

Iíd be very pleased for any kind of feedback.
regards
Erech
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  #2  
Old February 3rd 05, 06:30 PM
Christian McArdle
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Posts: n/a
Default

Will it be kind of one circle with the water being pumped around and
around?


Not usually. Most UK systems use a two pipe system with the radiators
plumbed in parallel. However, some older systems may use a one pipe system.
It would be quite rare, though.

If I remember rightly, the Radiator can be adjusted separately, so
there must be some form of a bypass or something.


That would be the case with the one pipe system. However, the standard two
pipe system simply cuts the flow through the radiator.

In May, I want to include a combination boiler into the system. Either
gas or oil, I havenít decided on that point yet (no mains gas).
How do I best go about it?


You need to bring the whole system up to date when installing the boiler. It
would probably be best to decommision the old back boilers (they may require
sand filling or removal). Then remove the hot water tank and associated
pipework. Finally, locate the ends of the radiator pipework and plumb these
into the combi, adding thermostatic radiator valves and a programmable room
thermostat. As it is a holiday home, which will be either unoccupied for
periods, or benefit from simple controls and low maintenance if let out, a
combi boiler would normally be a good choice.

If the system is currently one pipe, then you should upgrade to a two pipe
solution, which may require considerable repiping. Although one pipe systems
can be made to work, they are inefficient and difficult to control. The BCO
might not sign off such a system.

Is it Ok to blank the gravity feed and return pipes from the boiler in
the attic, or do I need to open the fireplace and blank the ends at the
boiler?


The exact steps to decommision the back boilers may vary. Some can just be
disconnected. Most need to be sand filled. Some will even need complete
removal.

I would very much like to keep the back-boilers operational for heating
purposes.
Is that possible?


It would be very difficult to combine a back boiler with the combi boiler.
The combi boiler will normally expect a sealed pressurised system, which
would not be appropriate for a back boiler. You would need to find a combi
boiler manufacturer that allows an open vented system and then connect the
back boiler in through a Dunsley neutraliser, or heatbank. I doubt this is
worth doing.

I assume that the heating will be run of the combi-boiler a lot of the
time. But when I light a fire I would like to have the feeling that Iím
not wasting a lot of energy.


The energy removed by the back boiler should not be regarded as otherwise
wasted. Even with the back boiler installed, you may get better efficiency
running off the gas/oil boiler than off the solid fuel. The back boiler will
increase the fuel requirements of the fireplace. The only reason to keep the
back boiler is because you have a plentiful supply of wood fuel
substantially cheaper than the oil/gas.

When the combi-boiler is heating the house, depending on the way the
central heating piping has been designed; the back-boilers would act as
a radiator warming the air in the fireplace and causing a drought up the
chimney. ???


This problem would be sorted by the Dunsley neutraliser/heatbank.

Iím thinking of a 3 - way valve which sits in front of the water flow
to the back-boiler.
In one position the water flows through the back-boiler and gets heated
by the fire
In the other position the water flows through the bypass and doesnít
heat the back-boiler unnecessarily.


Such valved solutions can be dangerous and expensive. The Dunsley
neutraliser or heatbank provide a much safer method of achieving the goals.

Should you really want to keep the back boiler, I would do the following:

1. Use a heatbank (this will mean you need space for a cylinder, but will
give you electrical backup and much better hot water).
2. Use a standard boiler (not combi). This can use the indirect coil of the
cylinder (if pressurised), or be connected directly (if vented).
3. Plumb the back boiler into the heatbank directly.
4. Run the radiators off the heat bank.

However, for a holiday home, I would still recommend that you use a combi
boiler and totally decommission the back boilers.

Christian.



 




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