I have a Vaillant Eco Tec Plus 418 condensing boiler at the minute installed in a upstairs bedroom cupboard. It's serving a conventional open system with a skinny 1050 x 400 indirect cylinder in an adjascent cupboard. That's as big a cylinder as i can get in there. I'm sick of low hot water pressure and not enough of it to fill a large bath so want to change to an equally good quality Combi. Obviously as far as i know their are no leaks on the system which i installed 5 years ago but, till i test it i can't be 100% sure. I was wondering if i could keep the heating side open on the F&E tank and still have the benefits of mains hot water. I've had no problems with my Vaillant so probably go with another if suitable. Or, should i bite the bullet and turn it in to a fully sealed system even if it means finding any miniscipal leaks? Any advice please?
No, you can't have an open system with a combi. The boiler contains all the components of a sealed system. The heating flow and return are connected directly to the boiler, and the system is then put under pressure. The new boiler MUST be installed by a Gas Safe installer, who will advise on the correct size for your needs.
First, a combi boiler produces endless hot water! But, you need lots of patients as the flow of hot water is very slow.... you could read a book from end to end in the time it takes to fill a large bath. On the other hand a copper tank as described, joined to the cold water tank and bath with 28mm pipe will deliver masses of hot water at low pressure, filling the bath before you can read the first page. That copper tank, with water at 60C or more is capable of doing what you want. Second, when someone flushes the loo, or turns on a tap elsewhere you loose what little flow you have.....this can really be annoying! Third, if you are having a shower.....you freeze.