New Boiler help?? - please - 'Main 24kw HE' Combi Condenser?? and converting 'Open Vent' system to Combi

[leeloo1]

We're having our boiler replaced (lucky us! ) and the insurers have said they'll fit a:

'Main' 24kw HE Band A, Wall mounted condensing combination boiler

Quick googling suggests this is a budget model and we may be better off offering to upgrade.

We currently have an 'open vent' gravity-fed system (amazing what you can learn via google!) with a 32yr old floor-mounted boiler and I'm worried that the new boiler will not be able to cope with our dreadful old system - and that it will require lots of work round the house. DH is also adamant that the work needs to be done without accessing the hot water tank - which is neatly boxed into an airing cupboard in his study by his electrical gizmos and a 42" tv!

If anyone has any boiler recommendations (or knowledge of this particular boiler) or has changed from an open-vent to combi system I'd be really grateful to hear from you.

If it makes any difference to boiler requirements or advice - we're in a 3 bed mid-terrace. :)

A combi has provides enough water on demand to give a good shower.

It will be rather slow to fill a bath.

Since there is no stored water, the maximum amount of water that can be delivered from all the taps in the house at any one time, will be whatever comes into the house through the water main. You can measure this by running the kitchen tap into a bucket and seeing how long it takes to fill.

For example, you might get 10 litres per minute. If you are running a 10l/min shower you will be quite happy, until someone turns on a kitchen tap, or flushes a WC, or the dishwasher draws water. Then the 10l will be shared between the outlets. You might get 5l each, or one may take more than the other. This can be quite tiresome.

A bath holds about 100-120 litres, so in my example would take 10-12 minutes to fill, except that at full flow, the water will not be as hot as if you turn it down, since the amount of heat delivered by the boiler will be shared out over less water. The water will not be as hot in winter.

If I was buying another boiler tomorrow, I would insist on a stainless steel heat exchanger. Iron is no longer used, and aluminium corrodes.

Viessmann and Worcester Bosch are good brands of boiler.

Oh I should have said - I have an electric shower and dishwasher and washing machine only have cold water inputs, so it'd be needed to run baths, wash hands, fill basin for shaving...

thanks for the comments. :)

although the other points may be using cold water, they will be using some of the water from the incoming main that therefore reduces the amount of hot water available.

You can get a good-quality condensing boiler that fits in as an open-vented conventional boiler as a fairly simple replacement of your old one. If you go that route you will retain a HW cylinder and you will not be restricted on amount of water delivered.

The Viessmann 100 Compact fits the bill and has a stainless exchanger and a 5-year parts and labour guarantee. I got one. The installation cost should be the same but the boiler itself may cost two or three hundred more.

I do not sell or install the things so this is not an ad or spam.

Plumbers will grumble because it is faster and more profitable for them to fit a Combi, even though the reliability of a combi is worse, and they deliver less hot water.