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nickjones wrote:It all sounds rather complicated to me, just buy another kettle Tim.

I do drink a lot of tea Nick lol

YYS4BOB wrote:If you don't want to go to too much trouble (removing cylinder/tanks etc.) You could go for a similar boiler to mine. This is a SYSTEM BOILER, not a combi

Ah! That was my mistake. When I referred to a hot water tank, I was apparently talking about a system boiler (which heats the hot water indirectly in an immersion heater style arrangement) rather than a combi boiler (which heats the hot water directly).
There are plenty of sites on the Internet which explain all of this, and also about the different types of venting arrangement.

I have a 20 litre insulated electric water heater that delivers tap or shower hot water kept at 60 degrees (prevent legionaires & other nasty bacteria from growing in water + pipes) and then have an oil or wood or pellet burner that heats water in 7 radiators to my own choice between 30-45 degrees depending upon how cold it is - if electric heater is off or out of water this also heats tap water as well with settings upto 70 degrees. I have discovered the electric water heater provides all the hot water the 2 of us need without the need or expense to run the big burner upto 60 degrees

SMS88 wrote:..and then have an oil or wood or pellet burner that heats water...

The problem with having a back-boiler in any kind of coal or wood during stove is that it inevitably lowers the temperature in the space above the bed. This results in incomplete combustion of the tarry materials released during the combustion process which are then deposited in the chimney as the gases cool. The presence of such tarry deposits significantly increases the risk of a chimney fire.

tjlglass wrote:So Bob are you saying a 30 combi boiler might be dearer to run than the old 1970's boiler I have at present.

Any modern machine will be a lot more efficient than a 40 year old one!

It's all about preferences I suppose. Personally I favour a hot water cylinder because it gives you the possibility of an alternative means of heating your water. I have an immersion heater in the tank as a back up in case the gas system fails for any reason. All new boilers are condensating machines, so need to be fitted reasonably close to an outside drain.