I bought a 04 plate streetka last month , firstly the heaters don't work at all but when the engine is fully warm you can feel a little bit off warm air coming from the vents and that happends no matter if the heaters are switched on or off , secondly the water / coolant likes to disappear . There's no wet patches under car so really don't understand where it's going . I need to fill it up everyday with water it's not overheating and it's running find but these two problems are really confusing as a lot off garages are all saying different things .

Sniff test , when you fill it up with water does it smell of petrol

Check your oil does it look creamy in colour on the end of dipstick, or oil filler cap.

do you see any white smoke from exhaust.

You thermostate could have failed shut , for the heater stopping water circulating

Your water pump could have failed stopping water circulating

From what your saying it could be head gasket or water pump leaking for the water lose.

Hi and welcome to the club.

Firstly I suggest you change the expansion tank cap. They are cheap and should be replaced at some point anyway. If the system is not holding the pressure it could boil off some of the coolant. It wont necessarily send the temperature up as it wont be circulating and the area that the sensor sits in may still be showing as cool.

You can test to see if the system is pressurised by running the car till its warm and check all the hoses are hot. Try squeezing these to ensure they feel hard as they should be under pressure. If they are soft then there is no pressure in the system and the coolant will be boiling way below its normal temperature.

If after you have changed the cap and if you are still not getting heat through the vents, you could have a stuck thermostat or a faulty heater control valve. Again the stat would be due a change now anyway. If it is stuck open you would only feel some warmth with the car stationary and the engine ticking over. It will feel colder when you start driving.

If its the HCV, these are less than £40 to buy and take about 30 minutes to fit. This is controlled by the heater control panel which is on the other side of the control knob in the car. It is electronic and operates a solenoid on the HCV which allows the coolant to pass through the heater matrix.

I am assuming the head gasket is OK as you probably would have noticed other problems if it wasn't

Good luck with it.

as said change expansion bottle cap first. on the heater part look under passenger footwell just below glove box there it a screw to remove then you will see a sort of heater part that tends to go. cheap to buy on ebay or it maybe the part thats on the bulk head that needs replacing