I've had weak or no heat after the Audi dealer replaced the timing belt and water pump in my 2004 1.8 A4. The mechanic claims that the problem is with the thermostat, but I had no problems with the heat before the service, the car does not overheat now (or before) and I see no coolant leaks. Makes me wonder if my problem now is not caused by the service.

I did not ask the dealer to change the thermostat with the timing belt and pump, but it seems that many people recommend this as standard (I did not know). Now the dealer wants to charge me $680 to change the thermostat, after I already paid $1,100 for the timing belt and pump. Should I go with the dealer's suggestion and change the thermostat? Try something else?