Pressurized Hot water for loft conversion

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.

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...

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.

I can only ask the question, would be surprised if not coz its just a 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

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.