Are we odd (no water tank)

Only if you suffer regular losses of mains water!

This is very often done when a combi is installed esp in a smaller property such as a flat.

Not really, gives some buffer against mains water being cut off..

The cold water tank was used as a supply for the hot water cylinder, now that you have a combi neither is required.

You should also be able to run your shower off the combi, depending on the flow rate, which would work out cheaper.

Dave Jones

By the way, why is this necessary? Why can't the hot water cylinder be fed directly from mains?

Martin

A standard cylinder would not be able to with stand mains pressure, and would split. A direct cylinder costs around 5 times more then a standard. So unless there is no space for a water tank the standard cylinder is the cheaper option.

The only benefit that I can see from a direct cylinder is mains hot water pressure.

Dave Jones

Just a small point. A direct cylinder is one where the water is heated by passing it directly through the boiler rather than having an arrangement with a coil in the cylinder with separate water that is part of the heating system water fed through it. These were more common when hot water was generated from back boilers etc. and CH not necessarily implemented.

A cylinder that is fed directly from the mains is referred to as a pressurised or sealed cylinder. THe copper is thicker, and there are arrangements with an integral or external pressure vessel or other arrangement filled with air or nitrogen to absorb the expansion of the water as it is heated. There are also pressure and temperature safety valves.

An open vented cyinder uses the tank in the loft to absorb the expansion and the safety is through the vent pipe going up and over the top of it.

Where a cylinder has a coil for heating the water, it is referred to as indirect and can be either open vented or sealed.

A sealed cylinder does have the advantage of not needing a roof tank (if space is of concern).

.andy

To email, substitute .nospam with .gl

See main FAQ. For flats a combi is now the most comon arrangement.

Since the combi is directly fed from the cold mains (and therefore all of the taps/showers in the house) there's no need for a cold water tank (or any other tanks for that matter).

Our previous house had a combi (Vaillant Sine 25W) and was excellent. Our current house has tanks and boiler (Ideal Standard [Stelrad]). Wish we had the Vaillant... sigh!

In what way was the combi better - other than space issues?