Heres 1 for you guys.  My parents in law's car plain refuses to start. It's got a brand new battery on it. It's also had a few relays replaced but the car still doesent want to start at all.
From what ive heard the starter motor spins but the engine doesent fire. 
It's a 1.9 diesel on a vw passat. I kniw its not a skoda but some one out in skoda land might have a clue.

Try squirting some Easy Start or Brake/ Carburettor Cleaner into the intake while it's being cranked.

 

If it fires you will know it's a fuel problem, possibly fuel tank pump.

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Why were a few relays replaced and by who.  As in what was the issue that required that?

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What relays?

 

Was the car fine before the battery replacement or was it failing to start, and who replaced the battery?

Edited 6 March, 20215 yr by e-Roottoot

My father in law replaced some of thr relays. I know one of them had a crack in it. 
the battery on the car was knackered so he replaced that as well. 

Possible fuel ie air or the fuel not getting to the very high pressure the PD engines require.

 

Bought a NOCO GB20 jump starter late last week, what a bit of kit.  Started my Megane Scenic and the went straight on to start a Focus ST with a flat battery what a bit of kit ! .

 

Good luck, may need someone with fuel pressure checking instrument  

 

VCD -PD error codes....   https://sites.google.com/site/1810martin/vcds-and-pd-tdi-engine-health-check 

 

Lack of firing could also mean that the mobiliser could be faulty and causing the car the fail - what era is this Passat? (year?)