[Warning Light] Oil light flickering after cam belt and water pump change

[wande87]

Dont know if anyone has already posted something similar, ive just set up account.
I have just had cambelt and waterpump replaced on my 2008 1.6hdi (90hp) at a garage yesterday, drove about 10 miles no problem then last couple miles van made a beep and oil light flickered on and off for about a second a couple times. I pulled up coolant was low (is this expected after water pump change??? Sorry i dont know much about cars/vans just the basics like how to change filters etc ) but oil was showing okay on dipstick. I topped coolant back up and checked for oil spills/leaks on ground and not seen any. I have only just replaced oil and oil filter myself couple weeks ago so today checked around filter for leaks and took filter back out to make sure the spigot was in the hole and filter was secure. Drove the van for about 15-20 mins today it beeped and flicked on fpr about a second once and that was it. Anyone else had a similar problem? Maybe the oil pressure sensor is on its way out or something has been knocked like a cable to it when it went in garage yesterday? Garage is closed till tuesday so going to go back then just thought it might be something easy and simple enough to do myself