Has anyone had to deal with a tyre that goes flat out of the blue then after inflating deflates again in 4-6 hours.

I have had the tyre replaced more than once but now think it may be the rim.

Either the rim or the valve. Try valves as they are cheap 

Also check for rust around the valve area ... its a common issue 

I agree with Piotr, check the valve and then check for corrosion on the rim. 

You've not hit any pot holes by any chance? 

2 hours ago, Steve Q said:

You've not hit any pot holes by any chance? 

Try not hitting one the UK roads are a disgrace and we have to pay road tax for poor roads, its a joke

4 hours ago, Paul A6 said:

Try not hitting one the UK roads are a disgrace and we have to pay road tax for poor roads, its a joke

Tell me about it Paul! Only 1/3 of our road tax goes on fixing roads. The rest goes to pay duck houses or fancy flats as part of MP expenses!