Thanks for the advice so far chaps...replies as follows;
Simond/Nixt - OK Ill put a primo back on my possibles list;
Doc Drivel; - Ethos looks impressive for a combi at 25l/min but thats the 41kw model...the 36c model is way down at 16l/min. Would it be much less efficient if i only need 30kw?
Not less efficient, just a lower DHW flowrate.
I currently have 3.5bar pressure but only a 15mm incoming main which gives me 20l/min at the first tap. It appears to get my money's worth out of any new kit i put in i need to upgrade it to at least 22mm...but i figure for the effort involved i may as well stick a bigger one in...28mm?...32mm?..so long as theres no downside to this?? How big should I go? Unfortunately the board's main is on the other side of the road and they have kindly quoted me £900 to upgrade their own rubbishy rusting little pipe....but if it gives me 30-40l/min ill begrudgingly pay it.
£900? Wow!!! Best abandon the unvented cylinder tripe and go for an accumulator and a high flow combi. An Ethos combi, or equiv, will go at floor level on the wall and the cold water accumulator will go in the cupboard. Then high cold water flows @ 3.5 bar.
Best have an accumulator. Explanation:
"The flow of water to taps from a mains fed system is limited by the size of pipes and fittings that the water has to flow through. Where you have no restrictions, and large pipes, it is possible to get a large flow, even with a low pressure.
The problems start when pipes are smaller that desired, and act as a restriction. Old mains supply pipes into properties are typically 1/2 inch and even with a good pressure the water simply cannot flow through the pipe in great quantities.
To the user this is seen as a severe drop in flow rate from a tap when a second tap is opened simultaneously. There is not enough water coming in to do both, so it gets shared.
An accumulator is a simple fix. It is a water vessel containing a balloon of pressurised air. The mains water squashed the air as it fills the vessel, until the air pressure increases to match the mains supply pressure. Now, when a second tap opens up, the additional water required can be supplied from the vessel, at full mains pressure, without the restriction there is on the mains supply.
When all the water charge in the vessel has gone, the system returns to normal flow rates, so it is important to estimate the size you will need based upon how much water you may need before all taps shut and the vessel can recharge.
Installation could not get any easier, with one connection anywhere into the cold mains pipework. A non-return valve is also needed on the incoming mains to prevent the charge from disappearing back into the mains supply should the local pressure drop temporarily.
They are maintenance free and DIY installable, and with typical prices around the £200 mark, you are unlikely to find a cheaper way to improve your flow rates to taps."
Go to No. 3
It stores only cold water. They are simple, very simple and highly effective. No need for silly tanks and noisy pumps and it does hot and cold too. It can go anywhere in the house, or in the attic of a garage. All it needs is a 22mmm pipe to the hot and cold water system. It could be fitted in an insulated shed at the bottom of the garden, way out of the way - just run one underground plastic pipe to it, that is all. It is the cost of just the pump to buy.