Pressurized Hot water for loft conversion

I'm planning to convert the loft to include a new bath/shower room.
I'd like to get rid of the big cold water tank which is only used to feed the hot water tank. I'm sure we can find space for the existing boiler header tank above the new radiators.
I have read the FAQ and don't want to change my current boiler for a combi because
a) Its only 3 years old, not condensing but reasonably high efficiency claimed, I'm sure it is big enough...
b) The boiler is in a utility room out the back I would expect a long delay to get hot water at basins in the bathrooms.
c) As the boiler is fed by a 22mm gas pipe that get there via a tortuous route through the house and kitchen (via hob and oven), I suspect it would need to be replaced with 28mm direct at considerable expense/ disruption.
d) We have hard-water and I concerned about reliability/ maintenance costs of a combi.
e) SWHTBO likes the airing cupboard. (but current old tank with jacket will be warmer than any modern replacement!)
I think I would like a "fast recovery" pressurized hot water tank. Is it OK to have a pressurized tank with gravity fed heating coil? The current boiler cannot be pressurized and seems to say this is not recommended only.
Is a pressurized hot water tank, gravity boiler loop only a sensible solution?
M
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What is this boiler, that it is 3 years old and has to be gravity (i.e. convection) circulated? Or do you mean just gravity fed, but with pumped circulation, in which case, any indirect cylinder of any type is fine.
I'm very surprised to hear that a boiler made in the last 3 years doesn't support pressurised operation. Do you have the make and model? If it can be pressurised, this is by far the most recommended route. It leads to quieter, more reliable operation and means you can remove your header tank, too. I suspect that you have a boiler that could be pressurised, but isn't, but I might be wrong.

Assuming you mean gravity fed and not circulated, then yes. You also have the alternative of a heat bank. The advantages and disadvantages of unvented cylinders versus heat banks has been done many times in the past and a quick Google Groups should come up with loads of stuff for you.
Christian.
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Sorry, I mean fed from a head tank with pumped circulation.

Its an Ideal Mexico, FF 60 installed late 2000. I've now found a statement that says
"The boilers are suitable, as standard, for connection to open-vented systems ONLY - an overheat thermostat kit is available to allow the boiler to be used on sealed water systems"
The boiler is rated at 30m static head so I guess that I could get an expansion vessel to run the system at enough pressure to fill a couple of radiators in the loft without a head tank but the manual also says
"Single feed, indirect cyclinders are not recommended and MUST NOT be used on sealed systems"
but should be able to locate the central heating head above the radiators, it a sink and a shower in the loft that is the real problem.

Thanks very much, now I have found the correct terminology I see that I probably want a heat bank. Pity about the extra pump and controls but not too keen on a certified pressure vessel with annual inspections and scale problems. Next problem is that the current airing cupboard not big enough...
M
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Is the kit still available?

The need for the thermostatic cutout is a safety thing to do with the fact that there isn't a continuous reliable feed of water. It isn't about the level of pressure in the system. Even some vented systems need a boiler with cutout, such as systems with combined feed and vent. The determining factor is that water must have a clear path to enter the boiler if it boils. If this can't be met, then an overheat cutout is required.

This refers to an ancient abominable form of cylinder that is no longer used.
Christian.
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thermostat which shouls be available as a spare if not identical on new models.

Please elaborate, it doesn't mean the strange ones I've just looked at
http://www.albion-online.co.uk
where the tank is filled with boiler water does it?
M
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No, it refers to cylinders known as "Primatic". Nearly all modern boiler manufacturers specifically disallow this type of cylinder which involves filling the primary circuit from the hot water cylinder through a perishable flap that allows all the nastiness in the boiler circuit to come out of the taps.
Christian.
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