I’m using a powerline AV500 in an extension via a lan cable and it keeps dropping. I think this is due to the central heating kicking in. The main sky box is fine.

Any suggestions how to get a good connection? wifi extender? 20m+ lan cable?

You need to run them directly in a socket. Not ideal in some situations.
I’m currently having cat5 cable run around the house as wifi signals can’t penetrate through the old exterior walls, and Powerline plugs take up too many sockets.

You need to run them directly in a socket.

You can run them off short extension leads, but make certain they don’t have surge suppression – that made my TPLink act up.

Straight in the wall is safer though.

Use a passthrough powerline adapter in the socket then plug extension into that!

http://uk.tp-link.com/products/details/cat-18_TL-PA451KIT.html

Do you mean in an extension to your house or on an extension cable?