Had cambelt and waterproof changed last week now.since that the heater is getting hot on the passenger side but only moderately warm on drivers side, I have notice a sound of bubbling when turn vehicle off towards the location of the heater matrix which was replaced earlier in year, issue only started since cambelt change.

Perhaps it wasn't bled properly?

I've been told these normally self bleed but I could be wrong 

You need to use VCDS to open up all the valves to do it properly. I assume they didn't do all that....?

No this wasn't done and don't know anyone with vcds software 

The garage you had the work done at?!?

They only have a texa diagnostic with no open to open valves or bleed checked today