Complicated central Heating; Back-Boiler and Combi-Boiler

[tfc715]

Hi,

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

Sorry I can?t give more precise information, but I live in Germany, an can?t investigate into the system myself at the moment.

In May, I want to include a combination boiler into the system. Eithe gas or oil, I haven?t 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 i the attic, or do I need to open the fireplace and blank the ends at th boiler? Or should I just short-circuit the pipes in the attic?

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

Or am I construction a Bomb?

I?d be very pleased for any kind of feedback. regards Erec

-- tfc715

[Christian McArdle]

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.

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

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.

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.

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.

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.

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

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.