Now with the colder mornings upon us I've discovered the rear windscreen heater/strips are not working.  Last year it was only a few of them but was not demisting at all today.  Any thoughts on a DIY fix for this would be much appreciated..................

Have you checked the fuse?

35 minutes ago, alexp999 said:

Have you checked the fuse?

No.  I know where the fuseboxes are but that's as far as my knowledge goes. What exactly am i looking for when i open them?

check fusebox diagram to identify fuse. Take it out and look at it to see if the metal goes from one side to the other or if it has burnt out in the middle.

As I have a voltmeter I would check if there is voltage at the connectors on the rear screen. also check the connectors are connected properly there. I have sent them break off the screen before which is a problem. 

I have no read all of this but it has some pictures:

 

https://www.frostfighter.com/defroster-repair-fix-it-guide.htm

2 hours ago, isetta said:

As I have a voltmeter I would check if there is voltage at the connectors on the rear screen.

I too have one.  When you say connectors on the rear screen, where exactly would i put the negative/positive prongs?

I have identified the fuse using haynes so will have a look in daylight and see.  Thanks mate!

Just to update:  I've repaired the small breaks i found in the windscreen and am now getting a voltage reading before and after so am confident that it is repaired.  Just have to wait to use it to be sure.  It was Granville electrical connector kit from Halfords for £11.99.  One question though.  I pulled the correct fuse for the rear demister (F105) found in the passenger glove box.  I did this to stop it coming on while the stuff was drying.  However, it didn't work - there was still voltage going across the rear screen.   Why was this?  Is there an issue somewhere?

8 hours ago, Albert27 said:

I pulled the correct fuse for the rear demister (F105) found in the passenger glove box.  I did this to stop it coming on while the stuff was drying.  However, it didn't work - there was still voltage going across the rear screen.   Why was this?  Is there an issue somewhere?

Sometimes if you measure a circuit that is open (wires not connected to anything), then a multimeter can pick up all sorts of odd voltages. Just touching a probe can sometmes give readings. So if the heater was broken, so there was no connection to ground, and the fuse removed, I thought the circuit might be open like that.

But I just checked the circuit diagram, and the same circuit feeds the mirror heaters, branching off after the fuse and relay. So the "live" feed to the rear heater should be well and truly grounded by those mirror heaters. So no floating circuit due to a screen heater break.

Try the multimeter on ohms range (heater off or fuse removed), and see if you can measure across parts of the heater circuit, on the screen or at the connector if you can. All readings, if valid, should be very low, 0 to 3 ohms, I would say.  If you get high resistance across the heater at or near the connector end, then I would suspect a wiring fault, maybe where the cable loom crosses onto the rear hatch from the body.

Removing F123 should isolate the mirror heaters, and allow the rear screen heater to be tested independently.

34 minutes ago, Tdci-Peter said:

 

But I just checked the circuit diagram, and the same circuit feeds the mirror heaters, branching off after the fuse and relay. So the "live" feed to the rear heater should be well and truly grounded by those mirror heaters. So no floating circuit due to a screen heater break.

Thanks Peter.  I don't have heated mirrors on mine - does that change things?   I've enjoyed playing about with the multimeter on the screen as electrics isn't my strong point, gives me something more to learn!

1 minute ago, Albert27 said:

I don't have heated mirrors on mine

What! Even my basic Mk2 LX has heated mirrors, at least I assume it does as they de-mist when I put the rear screen heater on, though I have never really checked!

In that case I would guess that F123 is empty. But it should still provide access to the heater circuit at the fuse box end. With nothing in F123, then one end of its socket should go live if the heater is switched on. With the heater off, you can check the resistance to ground from this fuse socket, it should be very low ohms reading. With a bit of wire and croc clips to extend the meter cables, you could also check continuity to the heater element from this socket, again it should be low ohms to anywhere on the element. If high to everywhere on the element, then there must be a wiring fault between fuse box and element. If low to one end, and high to the other, then there is still an element fault.

If low ohms to everywhere on the element, and the resistance to ground is high, then there must be a ground wire fault, though this usually has other consequences as it carries ground currents for other bits on the hatch.

  (I am making the, I hope reasonable, assumption that the actual PCB layout for the fusebox (PJB) is constant, and only the wiring looms and installed fuses change with variants!)