Hi guys, first post... Trying to get to the bottom of this overheating issue.

We we're gifted this little ford ka 1.3L run-a-round for the missus's first car by a family member and we're trying to get to the bottom of why it's overheating.

The car's in good condition 30k on the clock 2005 duratec 1.3L, we're still on the first tank of petrol and it's overheated twice in the last two back to back journeys. All no more than a 4-5 mile round trip.

Took the car to the garage worried that the head gasket had gone, asked the machanic to do a check and he's done a check and says it's fine. Noticed the coolant expansion tank had a few pinholes in it near the cap and was slightly misformed so had him replace it. He mentioned they just go over time and it's probably effecting the running temp of the car and hence why it's overheating. I asked him whether the thermostat was bad, and he gave a detailed reason why it couldnt be bad and mentioned fans coming on and heating working etc.. He said he'd run the car after doing the work and left it sitting with the engine on and it hadn't overheated. Unforuntately when we got it back, first journey, it's overheating again.

One thing i've noticed since we've had it is that it's always blowing hot air. Even when we set the cooling to cold it's still blowing hot air.

I'm starting to wonder after looking round the forum whether the heater control valve is bad? It makes sense to me that this part may have gone bad which is why the heating has stuck on HOT also the issue happens quickly within a few miles but ONLY under load of driving.

What would you guys suggest?
If it is the valve, what valve should i buy in the future to stop this happening?

Any info would be great.