Central heating alterations

Check the temperature and pressure ratings. The pressure rating drops dramatically as the temperature rises. Plastic also needs to be well supported if you aren't going to get excessive sagging, over time, between supports.

Is that likely to be a problem with any of the plastic plumbing systems though and even a pressurised system is only run at 1 bar or so. Hep2O and Speedfit are fine.

I've no experience with flopast, it looks similar to Speedfit, which is fine. They have their own website if yoiu want more info.

True, and I'd not use it in visible areas where appearance mattered. but it's easy to install and I find it useful when working in awkward areas

Why not just use solder fittings? I (like many) consider push-fit to be crap, especially on CH systems. Soldering really isn't hard, and will remain mechanically strong and leak-free for decades. Push-fit relies on rubber 'O' rings.

The problem that brought this about, was expelling water / steam in the existing pipework

IIRC the OP can't get the pipe dry...

There are always Cuprofit (IIRC) - pushfit for copper and the fitting is brass. Can be demounted wiht a special (but cheap) tool. Still has o-rings, but is otherwise bomb (and mouse) proof.

Solder the joint up dry on the bench, then attach it to the system with a couple of push-fits... ;-)

If you've got mains pressure hot water, that can get a fair bit over 1 bar. (Without checking the ratings, I don't know if it's likely to be a problem.)

Yup, they work ok, bit pricey though...

The fittings yes, the pipe no. Not been that impressed with FloPlast fittings - they seem to need quite high insertion forces to get a properly seated joint, and they are not at all tolerant of any misalignment on entry.

The pipe however may well be fine since I can't see much they could do wrong with that!

Temporary fit Speedfit here - 4.5bar pressure on the hot water side, up to

I can't remember now without looking it up, but Hep2O was fine for the mains pressure water in our old house - and that had pretty high pressure.

Of course this ha smade me go and look it up :-)

for Floplast it gives a max working pressure of 12 bar at 20C

at 85C, 4 bar

Anecdotally, no. In our old house I used it quite a bit and it had mice but we had no problems with nibbling. I've had abit in this house for a couple of years (running a temporary replacement supply out through the old stable and that's also fine.

I have seen copper pipe fail after less than 20 years and fittings that never worked, I have yet to see any plastic pipe/joints/fittings fail even in heating systems. I have plastic pipe in my heating system, its ~29 years old.

So says the bloke who still see the fairies in the bottom of his garden.

Hmm. In the middle of the night when the mains pressure might reach

This is true. One set of boiler installation instructions I read said to take the last bit (1m, IIRC) in metal pipework and not plastic.

That is to limit damage when the boiler decides to keep firing after the stat has broken.

I had to rectify a cowboy's work on a new boiler. The tosser had connected the Qualpex right onto the boiler. It had lasted three months or so, which surprised me.

I think that is the recommendations of the plastic pipe makers as well.