Heating system died

[cambridgepolodriver]

I have a 1989 G regd Polo 70,000miles. Tatty but never let me down. The heating has suddenly gone, boooo. Happened pretty much overnight. Working one day, not the next. I've tried the slider switches in all combinations and that doesnt do anything. When it died, it came back temporarily for about 5 minutes when i waggled the sliders. Then died again. Since then, it's been permanently broken. In this wet cold weather, not nice. I've got a Haynes and am reasonably handy with a screwdriver. Question: is this a straightforward repair? Are there bits on the heating system that are prone to wear and tear, breakdown that i should be looking for? Could it be something really simple - like a fuse or whatever. Any observations and advice very gratefully received.

[steveo3002]

lift the bonnet and yank off that black plastic tray up near the wipers

you will see a lever on the passenger side that the cables operate...see if thats moving with the internal levers

other than that..see if the hoses are getting hot etc

[mk2matt]

do what ^^^^ he says

if its the cables its a bastard to fit cables inside the car with dash still there

if its the pipes blocked, take them off and let them dry out and roll them on a hard surface to loosen the crap off and rinse them out
or find a bottle brush and wash them out

then refit

[cambridgepolodriver]

Thanks for your useful feedback - just as soon as it warms up i will take a look under the bonnet.
But meantime, i discovered something odd - which people might like to speculate on?
Most of the time i drive the polo around town so never get much beyond 40mph. For the past two months, the heating has been well and truly non-working.
However, coming back from the coast yesterday i noticed that when i drive above 60mph in third or 40 in second, the heating comes on, hot as ever. As soon as i drop the revs (and speed) or change up, the heating goes off.
I find it really weird that the heating is linked to the RPM. Anyone got any insights?
Cheers

[steveo3002]

thermostat maybe?

[alexperkins]

Could be the water pump or something - faster RPM means faster water flows around the system.

[pitman]

If the thermostat worked before but now is always open (better than always shut ) you could check this with the temperature gauge on the dashboard.