replacing plastic pipes with copper

[johnopaulo]

I am re doing my bathroom (still) and since my original leakage problem being because of varying reasons I have taken up all the floor and found that all the plumbing is plastic. I have read many differing opinions on using plastic and copper pipes. I live in a farm area and we do have rodent problems. Gien that and the age of the house I would not be surprised if I have them under the house seeing as there was a couple of dead bird carcasses found there.
Anyway, I have decided to replace the pipes in this area with copper (15mm) and my question is the hot water supply. There are no visible isolation or gate valve shut off valves on the pipework into this area. I have a radiator at one end of the bathroom area and a hot feed going to or coming from a radiator in the adjacent room via plastic pipe through the originial sandstone foundations.
The cold water feed is already isolated and the cold taps and cistern are empty. But will I have to drain the CH which is upstairs and at the furthest opposite point to this bathroom which is downstairs and at the extreme opposite gable end, or is there an easier way, I am thinking to locate the hot flow into the area and put an isolation valve on it at point of entry then I can get all the platic changed?
And is there any other considerations such as regs regarding pipe fixing to joists etc that I have to be aware of?

Thanks
Johno

 

[Axel]

Don't confuse the central heating pipework with the DHW (hot water to taps) pipework...

 

[johnopaulo]

the radiators and towel rail are all plastic pipe as well as the pipe going to the sink and bath and they all look to connect to each other in this mess of pipes. And not one single pipe has any ident marks or even a hint of direction ar usage. As i said the old water turns of asily from an outside riser just outside the bathroom window. It only shuts of the water in this area and does not affect the rest of the house.

Johno

 

[digdilem]

While I'm not sure I'd agree with you on your logic about replacing them (I'm also very rural, underfloor plastic pipes laying on the ground - no damage yet, unlike the copper CH pipes which got over-fluxed and have pinholed in several places under the floor). Personally I'd leave proper working pipes alone. We also use a lot of MDPE, similarly nibbly to rodents, and despite being responsible for literally miles of it, I don't recall a single instance of that happening. The only animal damage to mdpe I get is from horses, and I don't /think/ I have any of them crawling around under my house. More risky IME is rodents in the house on wiring, now I have seen a lot of rodent damage to /that/ including when it makes the big blue sparks fly - so if you are worried, put down some poison instead.

Anyway...

Identifying hot water pipes is easy. Turn on a tap and see which one gets hot. If you hold it in two places an arm width apart you can even tell which gets hot first and so determine direction.