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After removing the damaged pipes from the coolant system yesterday, I topped it up this morning and watched it run for a bit to see if I could see anything coming out anywhere else. I couldn't.

But what I did notice was the fluid cycling through the header tank as soon as the engine started. Is that normal? I wasn't expecting it to start cycling until the engine was up to temp and the thermostat opens, or is my mind stuck in years gone by?

I'm also concerned that the fan isn't working, so I'm going to check that tomorrow morning too, but some advice about the thermostativ valve, or apparent lack thereof would be appreciated.

Polo 1.4 Tdi BNV as mentioned previously.

Cheers guys!

Yes thats normal

Fan wise, thats controlled by a thermo switch in the radiator

OK, so I've put it all back together, set the engine away, and now I've got an engine management light on.

I did keep the air filter box off when I first started it, so I could get a good view of the new parts to make sure they aren't leaking, but I've put all that back in now, and the air flow sensor was literally the only thing I've unplugged.

Any ideas? It wasn't on yesterday when I was driving around with the hoses bridged.

If you didnt plug the air flow sensor in, youll get an engine light

It could however be one of many things. Really needs a scan and a reset if appropriate.