If you have tanks in the roof space i.e. a big tank and a small tank plus a cylinder in the airing cupboard then you will have a vented system. If you have a combi boiler this would be unvented. Also, some cylinders are unvented as well so you will need to check that. The lack of tanks in the roof space would normally confirm your system to be unvented. Which ever you have when you drain down an unvented system you will need to repressurise when you have finished. In a vented system you must make sure you isolate the ball valve on the small tank when you drain down so that it doesn't keep refilling. Finally make sure you add inhibitor on completion - Sentinel X100 or Fernox F1 are both quality products. Hope that helps.
Yes this is fine, make sure you isolated all incoming supply pipes and drain down as per usual.
The type of system you have depends on whether your boiler has its own expansion vessel or do you have F&E and cold water storage tanks in your loaf?
Do you have a combination boiler? Or a conventional boiler which serves your HWS Cylinder?
If so you will need to drain down both cylinder and boiler.[/quote]
Thanks for the help everyone. I have 2 tanks in the loft, but the council fitted a combi boiler a couple of years ago before we bought it from them, so I'm not sure if the header tank anf F&E tank are still in use. I don't think hey are. I'm not sure if it a conventional combi, because our hot water is not instantaneous. We still have to wait for the water in the storage tank in the airing cupboard to heat up. Our combi doesn't have the option of topping it up ie. there are no valves on the pipework running to or from the boiler.
You have a strange system here. Tanks that are possibly redundant and a combi which supplies your hot water cylinder.
The idea of a combi is to provide you with hot water instantaneously, whilst also satisfying your heating load. I cannot see why this type of boiler would be supplying LTHW to your cylinder.
Have you checked to see if the tanks in your loft are in working order? Do they have connected mains cold feeds with a ball valve to them? Or have the tanks themselves been drained down. I think this needs to be checked first to determine your system.
I am only a young engineer but as far as i know, combi's are a replacement of conventional boilers that were used to supply domestic hot water services as well as your heating supply. Maybe others have a view on this?
Are you sure its a combi and not a old type conventional boiler which is feeding your cylinder, this would make sense bearing in mind you stated you had to wait for hot water to be provided. Combis are instantaneous!...
Hope this helps you, maybe you can get back to us with some more answers.
Thanks for the advice cookie85. I will have another look when I get home. I will find the operators manual for the boiler and let you know the name. I know its a Baxi, but I will have to check the model.