Convert standard HW/CH system to Combi Bolier

I have got an old potterton bolier providing DHW/CH via a cylinder and header tanks. The boiler is an old cast iron one and is absolutely fine but at some stage it will need replacing. The obvious thing to do is replace like for like and continue with the system I have got. The other option is to replace with a combination boiler and remove the old cylinder and tanks to create extra space in the bathroom and loft.
I'm prepared to give this a go myself if the sequence of events is logical. What considerations are there in converting from the old system to combi boiler? The pipework will obviously change but not to drastically. The pump is upstairs in bathroom. This will need to be removed as new pump will be in combi downstairs. The cylinder and header tanks will need to be removed and relevent pipework reconnected. Will taps, cistern washers etc need uprating?
And finally if I do go down the combi route, what size/type would be recommended for a 3bed 3reception house currently let out as a 5 bed 1recepion with 1 kitchen and 1 bathroom (with electric shower, which I could convert to thermostatic).
Any help gratefully received
Charlie
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Charlie wrote:

a) Unvented mains cylinder + non-combi boiler. - if that is beyond the budget which will likely need a water main upgrade. b) Vented mains cylinder + non-combi boiler.
Combi can and sometimes are fitted to this size of house but that would be a personal choice rather than standard practice.
You don't have to have a combi to get many of the other benefits like sealed primary etc.
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wrote:

What cistern washers? The WC cistern will currently be fed from the cold rising main, only hot taps will be affected. If the cold taps are currently OK the hot taps will probably be OK also (same age).

Ed if his 5 tenants are currently happy sharing a single electric shower why make waves? (Sorry weedy pun!) They must be intrinsically very clean people.

It's not a 5 bedroom executive residence with 5 en-suites, it's a 3 bed house turned into 5 bedsits, the boiler still has the same number of simultaneous outlets to service. Anyway, bedsit denizens can only expect bedsit standards.

It's questionable whether anything really needs to be done. I would personally be happier with no tanks in the attic, especially in a house rented out, would anyone know what to do if something went wrong in the attic?
The existing cast iron boiler might run for 5 - 10 years more without problems, and be cheaper to repair anyway, a combi might break down 2-3 times in that period.
DG
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There again the combi will probably be perfect and old clunker break down a lot. Combi's are no more or less reliable than any other "system".
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What is this standard practice you are on about?
Unvented cylinder? A vented heat banks is far superior in many aspects. many councils have been bitten by unvented cylinders and are going overflowless heat bank.
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Charlie wrote:

The mains water feed to central heating loft tank was connected to what used to be ch feed pipe and was now connected at boiler end to cold water inlet for hot water. The combi hw outlet was teed into the hw pipework at a convienent point. The ch feed and return were connected to new boiler same as old one. The cold feeds that were fed from the large loft storage tank were fed from the mains.
The vent pipe, pump and hw cylnder and loft tanks were redundant.
After switch on the only problems were the odd seeping rad valve that didn't like the new sealed system pressure, cured by spannering and the Fernox stuff you can inject into a rad bleed valve, the odd toilet washer valve that had to be changed from low pressure to high pressure type.
The shower was changed to a Screwfix trad mixer type and this is very good on the combi output.

perfectly ok for a 1 shower setup. I used a Vokera boiler mainly because it was inexpensive and it has a rear entry flue which looks neat. Supplier was mrcentralheating.co.uk, you have to phone them up to get boiler only prices.
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