V70 Heater Blowing Cold

Sounds familiar. I had a similar issue with my old Saab 9-3. Was the coolant level okay? Did you check the heater core?

Coolant level is fine. I haven't looked at the heater core itself yet, though. Is it worth investigating that before I check the water valve wiring?

If the coolant level is fine and the error points to the valve, and you feel the cable or connection is faulty, it's worth looking into. But honestly, I'd get it to a shop. With the Saab, the valve itself was defective, and diagnostics would have taken me ages.

I booked it in. You were right – the water valve was defective; diagnostics confirmed it. Cost me 95€, but at least it's sorted. Thanks for the advice!