I've changed the heater matrix on my car but it's still blowing cold air?

I have changed the heater matrix on a 2012 VW Golf and the heater is still blowing cold air, what else can I do/check?

Honda CR-V heater on driver's side does not warm up, how can I fix this?

Having done the due dilligence (HJ Reviews etc) I took a 13 plate Honda CR-V for a test run two days ago which was a warm day so was pleased that the air con was running nice and cold (or so I thougt)....

How much will it cost to replace my Ford Focus' heater matrix?

How much would it cost to replace a heater matrix for a Ford Focus 2011 model?

How much work is required to replace a heater matrix?

I have a 2015 Ford B-MAX and water is coming into the driver's footwell. Our nearest Ford garage (which has been very good and I trust) has told me that it is something to do with the heater matrix - either...

My car only blows cold air from the heater - what's the problem?

I have a 2010 Vauxhall Astra that is blowing cold air only. I have checked the coolant levels and they're fine. What could be the problem?