I want to create a 4 layer pcb with signal on top two layers, then ground and bottom my ac heater runs. How do I do this?
What specific KiCad related issue are you having problems with ?
The default KiCAD project is actually 4-layer. The copper layers are: Front, In1.Cu, In2.Cu and Back.
So just lay the track as you want on those 4 layers. That’s it.
KiCad supports up to 32 copper layers, so that is plenty for your need.
What are:
If you want to use a copper track as some heating element, you can (ab)use the length matching tool to create a very long serpentine track.
If there is anything else you want to know (about KiCad), then ask more specific questions.
I have 2 pairs of heater lines feeding my tubes.
A245/A45/A65 & B245/B45/B65 lines feed my tubes.
Using Kicad 8 and free routing, I try to assign these net classes to one layer, ok, but when run other layers show up on this layer. I want these to be the only signals on that layer. What am I doing wrong?
So can these four lines as net classes be assigned to the same layer
Tubes? Do you mean those obsolete light bulbs? I guess that would make “heater lines” the filaments of those light bulbs. I guess your main trouble is attempting to use freerouter. I guess it’s just a handful of tracks, and apparently you want to reserve a whole copper layer to that, so it would be about 2 minutes to draw them manually in KiCad.
Hint, try this:
- Place mouse cursor over a pad.
- Press x to start laying a track.
- Press f to finish the track to the nearest connection.
- Re-iterate with the other tracks until done.
Trying to understand what a thread is about…
Tube and pipe translates to the same word in my language.
And the heating is mentioned from the first post.
So I suppose that may be OP is speaking about Heat Pipes - closed at the ends copper tube (with some fluid inside) that can transmit heat several times faster compared to be entirely made of copper.
The pictures of such heat transmiting tubes you can see here:
I suspect by tube they mean thermionic valves. A search for A245 gets this:
I honestly wouldn’t waste a layer on conducting heater current. You’d need sockets for valves so just connect the heaters with point to point wires.
Yes, “tubes” is american / international name for something what Brits and Europeans called “valves”. And they do need heaters voltage.
So, that’s probably what the OP meant.
Because of word ‘lines’ in:
I understood A245 and so on are the net names of tracks that feed (=supply?) something, or may be feed (=conduct?) heat to the tubes (=pipes?) which led me to the idea of heat pipes.
If ‘tube’ were not used alone (what for me means pipe) but with ‘electronic’ then it would be clear that the thread is about ‘electronic tubes’.
Fortunately when using transistors I need not to say electronic transistor to be clear 
I slowly begin to think that ‘conducting heater’ has nothing to do with using bootom copper layer for conducting heat released in the valve out of the place of this heat is released.
Association…
When in 1982 I was doing my oscilloscope I was afraid that mains overvoltage can damage my oscilloscope lamp ruining a whole year of my work so I supplied its heating through voltage/current limiting circuit.
In Finland we use “putki” which is literally “tube” (or “pipe”) while valve is “venttiili” which is a mechanical system only, corresponding to Valve - Wikipedia. Finland is part of Europe but not part of Great Britain. 
In Poland we use ‘lampa’ which is exactly lamp (like street lamp, bedside lamp, room lamp). If the context is not clear we use ‘electronic lamp’. Tube, having different direct meaning, is hard to associate with an electronic lamp.
You missed my point. The heater circuit is for vacuum tubes Kt88 & 12BY7A.
The heater feeds two pins on each tube. One heater pair feeds 2 Kt88 pins 2,7 and 3 12by7a pins 4,5 & 6 tubes. I want this circuit on one layer , with my audio circuit on the top two layers. Please tell me how to do this.
You still have not figured it out after two weeks? Did you read the manual
But where is the problem?
You can set the PCB to 4 copper layers with: PCB Editor / File / Board Setup / Board Stackup / Physical Stackup / Copper Layers (drop down box) and then the [OK] button.
I assume you already have footprints for these lightbulbs, and I’ll also assume these have footprints with THT holes. If so, then simply click on the layer you want a track to start on before strarting a track with the regular x key.
Assuming the PCB Editor is configured for four copper layers as paulvdh mentions above then refer to the appearance manager on the left right side of the PCB Editor window. Select the Layers tab and then select the layer that you want to route the track on.
The B.Cu layer (Back Copper layer) is shown selected in the following image.
I agree with you that we probably miss your point.
I still don’t understand what a problem is about.
You want to route 4 wires (two pairs) at bottom layer. And what kind of problem do you have with it?
When you have footprints located as you want them you have connection lines showing you what connections should be done. You select bottom layer, locate mouse at one of heating circuit tube pins press ‘x’ and route track to the right pin of next tube and so on.
The problem with routing arises when you have to do lot connections at one layer but with 4 there should be no problem.