Hot water tank drain. Can it be plastic?

[Tim Downie]

Our hot water tank has a drain that needs to be permanently moved due to work on an extension. The existing pipe is galvanised 15mm (or perhaps

1/2") that's a bit rusty where it's been exposed to the elements.

I could just cut it back a bit and extend it with copper but I'm wondering about replacing the whole pipe. Unfortunately, the route is sufficiently weird that doing it in copper would involve a lot of hacking and cutting of floor boards & joists. (There's a swan neck bend in the pipe inside a partition). I could potentially squeeze a plastic pipe (polybutylene or similar) through though without too much trouble.

Is plastic allowed in this situation? I know CH drain pipes all seem to be copper so I'm guessing possibly not although clearly plastic pipe can cope with the temperatures.

Tim

[Jim Alexander]

Don't see why not. Polyb pipe is spec'd for central heating which is a higher temperature spec than domestic hot water. I have a brass drain spigot on my cylinder. In the unlikely event of having to drain the cylinder I indend attaching a garden hose to the spigot.

Jim A

[TMC]

Tony

[Tim Downie]

That would be simplest undoubtedly but as it has a drain plumbed to the outside (that might be worth preserving, I was wondering if building regulations have anything to say about it.

Tim

[The Medway Handyman]

Plastic pipe is used for CH radiators so I can't see a problem.

[Onetap]

I can't imagine why a hot water storage cylinder would have a permanently piped drain; can you post a picture somewhere? The exception being an unvented cylinder which has a drain from the 2 PRVs; that wouldn't usually be galvanized and it can't be in plastic. Can you clarify what you're talking about?

[Tim Downie]

Rest assured it is a drain (with a draincock) but I've decided to stop fretting about it and just chop the d*mn thing off. Considering how often I plan on draining my tank, a hosepipe down the stairs will work just fine.

Tim

[Onetap]

It is not good practice to mix metals, so you wouldn't normally have a galvanized pipe connected to a copper cylinder. I'd suggest you also check the threaded fittings in the cylinder bushings. They should be bronze; iron fittings are sometimes used and they corrode and eventually fail, usually causing much damage.