Thinking of replacing a traditional vented cylinder (with header tank in the roof) with an unvented cylinder. It would be a straight replacement of the existing cylinder so everything in place already (downstairs location with good access to rising main, power, etc.).
Very roughly how much would I be looking at for fitting if I were to supply the cylinder?
Also, anybody got experience of Ariston [primo] cylinders – any good?

As long as you go for a stainless cylinder, over a vitreous enamal one, they're all much of a muchness really.
The various manufacturers will tell you their product is best because of x y y etc.
Have you checked your incoming mains pressure and flow rate? You definately need 1.5bar plus, ideally 2.5 plus. Flow rate needs to be 20 litres per min, minimum. Ideally 25 plus.
I've just qualified to fit these, got sick of paying plumbers to screw them up!
I usually charge around 300 quid, but it depends on a few things. An unvented cylinder needs a waste outlet, this can be the most difficult thing to get right.
It also needs wiring in properly, which I get a sparky mate to do. 9 times out of 10, he needs to re wire the heating controls as they are not done correctly.
I'm in the manchester area if you want me to take a look. I can also get hold of the cylinders at a fairly decent discount too

Interesting. I was going for a stainless one anyway, I like the idea of the big warranty.
By 'waste outlet', is that the overflow to outside? If so it should be really easy as the cylinder would be fitted in a cupboard with an external wall and a drain right next to it.
We'd be going for a direct cylinder (no central heating) so no heating controls involved.
Not checked but the pressure is very good and I'd be amazed if the flow rate was below 25l/min.
I'm in Chester but the property in question is 100 miles away in Abersoch so unless you fancy a day trip it might be a bit too far – shame as I'd rather use someone like you than a local plumber as they tend to never turn up when expected. 🙁

Direct cylinders are a bit cheaper, due to not having a coil.
Sounds like an easy fit, what size cylinder are you going for? You'll need about 600mm free space above the cylinder also, for the expansion vessel. It needs to be above the inlet controls, and ideally above the cylinder too, although it can be around the same height with some models.
It is a bit far, but if i've got nothing on, I don't mind traveling. It's been quiet since christmas, only just starting to get going.

from experience, use stainles if possible, Ariston are at the cheaper end, prefer Oso myself. Very good product but at the dearer and of the market.

Thinking about 170-200ltr sizes as that's about the biggest we'd fit in the cupboard.
Not heard of Oso – got a Megaflo here which has been good but hoping to spend less as the property isn't used continuously.

How big is the cupboard? Most unvented cylinders are approx 550mm diameter, they just get taller.

My email is in profile if you want to talk direct.

Door into the cupboard is about 570 I think then widens slightly. I'll drop you a line.

Oso do a slimline unvented cylinder. They are similar to Megaflo, outperform them in some areas, not all, but are cheaper.