One oil boiler feeds two systems??

Is it possible to have one oil boiler feeding into a house and a granny flat.....working off different fuel tanks and independent of each other. In the house it would only be a back up in winter but would be the primary source for granny flat.

It's definitely possible for one boiler to feed two houses... simplest is to have two pumps (or more) to split the required heating into zones. Two tanks is too messy... Unless you intend to have two manual valves for example where you choose which tanks is feeding it.

It would be possible to have two timeclocks, one in each house and to have those independently control the boiler as required.

Definitely the best way is to have the granny flat as a separate zone. You will only require one pump as long the main part of the house is zoned also and when heat is called for in the granny flat, it does not heat the main house and the pump is sized correctly to be able to pump both dwellings at the same time, otherwise a second pump will be required. Also ensure that the boiler can handle the extra capacity too.

With regard to oil tanks, this is more complicated and certain regulations will have to be met. For example, a bunded tank must be used as it is supplying a property other than a single family dwelling. It will also be more difficult to separate which oil tank is being used. For example, when both dwellings are calling heat heat at the same time, which tank will be supplying the one boiler?

Thanks guys. ya id like to run it off the same boiler and pump and creating the house or granny flat as a separate loop seems the best idea...I will only have 2/3 rads in main dwelling and granny flat isnt that big...standard converted garage. I would still love to be able to separate the fuel supply for each house....any ideas?

Given what Shane007 and the others have posted about the complexities, I'd imagine it would be cheaper install a second boiler.

Thanks leo so two boilers with a double tank maybe....still shouldnt be that much more expensice with a pump thta size 400 euro or so

You could put a solenoid valve on each supply from the tank to the boiler, that will be link to their respective zone valves, but as shane07 says, if they are both on which will supply the oil, in this case both solenoid valves will be open if both zone valves are open. You will have to make sure one of the solenoid valves is open before the boiler starts otherwise you will lock out.