Have a saab 9-3 vector sport 1.9 tid 2006 - heater is blowing cold, have tried to flush system but has just made it colder. One hose is hot the other cold so don't think its the thermostat. any advice welcome.

I had the same problem on my 9-5 vector 3.0 TiD with the top up coolant warning. Nearly became bankrupt trying to diagnose the problem and trips to Saab. Header tank, sensors, pressure tested etc. The Saab squaddies couldn't figure it out until it got worse. It's a head gasket failure despite passing pressure tests initially...sounds like it's still early days on yours. Had to replace the engine for near £5000.but under warranty :-) Reckon 2.5-3k at a good specialists.

heater control valve shot

try back flushing your heater core find the 2 hoses to the heater and start the motor let it run for a bit feel the hoses 1 should get hot and 1 should be a little cooler the 1 that gets hot is the inlet and the cooler 1 is the outlet remove them after the motor has cooled down and use a garden hose to back flush the core flush water through the outlet you dont need to use high pressure if you do there is a chance the core can crack and leak.

OK, most cars have heater cores that get hot but the blender door directs air away from this core in the a/c mode when you want cool air from the evaporator.

I'm not sure if there is a control valve which stops the water from going through the heater valve.

I think the part is called a 'heater blend door actuator' that you are after.
http://www.autoanything.com/air-conditioning-65-861/201A1060.aspx?kc=AFFCJ&mr:referralID=c9ca506d-9f22-11df-bf8d-0026b95a1738

I suspect you have a problem in the security system receiver module, which in most cars must be programmed by the dealer.

Check you have coolant flow to the heater core - feel the inlet and outlet coolant hose as near as possible to the heater core- they should be both be hot and approx equal in temperature.
If the outlet hose is noticably colder you may have a blocked heater core ( a reverse flush with water from garden hose may fix it).
Check the cooling system has been properly filled, with the heater coolant valve open, bleeding off any airlocks as required.
Check any cold/hot air re-direction vane within the cab heater air ducting is operating properly (not seized or stuck).

try to back flush the heater core. and if that dont work check the blend door it see if it is working.

You would change t/belt at 5 years or 100,000 miles.

check EGR,MAF,injectors,high pressure sensor(fuel)

I spoke with the Saab dealer whom sold me the springs last March, he told me there is an ongoing problem with many owners having to change springs, I have bought 2 x new springs and had them fitted total costs incl repair of damaged tyre £450, I will not be as originally planning purchasing another Saab, after sales are poor and excuses unacceptable when requested they honour warranty.