advice on best type of boiler?

[ThursdayNextIsMyHero]

Hi, we're upgrading our boiler and are getting confused what type of system would be best for our circumstances. We currently have an older boiler with a small hot water tank in the airing cupboard and a cold water tank in the loft. We have one bathroom (with a standard over-bath/non-power shower) plus a downstairs loo. There is no en-suite but in the future we might want to install an extra shower. It’s a four-bedroomed house, but not large, with 10 radiators (the rads are okay and won't need replacing). The boiler and hot-water tank are situated close together. The water pressure is apparently okay, more than 10 litres per minute measured from the garden tap, so it is suitable for a combi boiler (which surprised me because when we ppreviously changed taps on the bath we were told to go for ones suitable for extremely low pressure).

There are four of us in the house, and at the moment the system we have (in terms of availability of hot water, etc.) is okay, but we know that as the children get older, demands on hot water will go up.

There are three different systems we've been recommended: a systems boiler with hot water tank; a systems boiler with a pressurised tank; or a combi-boiler with no tank. The idea of getting rid of the hot-water tank and gaining some much needed storage space is appealing, but then someone else has said that combi-boilers are more recommended for smaller properties or fewer people, so didn’t know whether it would stand up to our current or future requirements. We’re getting some quotes, but seem to be getting different recommendations - some saying that a combi boiler would be fine, another saying a systems boiler and pressurized tank is the best, another recommending keeping the hot water tank and just replacing the boiler as a pressurized tank isn't required. We seem to be going round in circles, and don't know what would be best. What system do you think would be best for our current and future circumstances?

[PigletJohn]

four people in the house, I'd recommend an unvented cylinder running off a system or conventional boiler.

if the pipes and radiators are old and liable to split or leak, a conventional boiler will be less likely to cause it, if open vent. Many gasmen think them old fashioned, but it's not their leak.

10 litres per minute is not enough for 2 bathrooms.

Find your incoming water pipe; determine if it is lead, iron, copper or plastic, and its colour and diameter please.

[ThursdayNextIsMyHero]

I think the incoming pipe is copper and approximately 18mm diameter. The house is about 30 years old. The flow rate from the outside tap was around 10 litres in 20 seconds, I cant recall exactly but I know that it was faster than the bare minimum 10 litres per minute.

I'm completely showing my ignorance here, but is an unvented system the same as a pressurised tank? Like a megaflo?

[PigletJohn]

is it 15mm?

If you get 30 litres per minute, that is satisfactory.

Unvented Hot Water is usually taken to mean a hot water cylinder at mains pressure, such as a Megaflo, which is a well-known brand name, like Hoover.

[ThursdayNextIsMyHero]

It might be 15mm, it was awkward trying to access it, but it was definitely less than 20mm.
So the unvented system is the one that doesn't need a cold water tank?

[PigletJohn]

yes