Car been suffering really badly with condensation recently. It's worse when I put the heat on and did notice a drop in coolant. Suspected a leaking heater matrix blowing damp air around so today printed out of the 'how to' and had a go.

Bit of a pig of a job but got it out and new one in (with new seals) and it's not leaking and blowing nice hot air..

The only issue was the old one looked fine and there were no obvious leaks or corrosion on it!! it didn't look like it was actually leaking...?

Hopefully that was the culprit but what else might cause really bad condensation? Ta

Well done!

Did you notice any oily residue on the carpet in the footwell?

Other causes could be water ingress through damaged door seals, or from a torn/missing shower screen (membrane behind door card).

Check each footwell for damp carpet.

I believe a clogged cabin air filter can also cause this. It’s located beneath the scuttle panel.

Edinburgh, there was a bit of wetness on the funny little bit of carpet that covers the airbag module in the middle but not as much as I would have thought, footwells are dry but there might be a drip from passages door seal. Have checked the door membrane but nothing obvious.
Also plumped up boot seal with electric flex, only other area is the sunroof even though that has a new seal too...out of ideas!!
Hopefully the matrix was the issue!!

Hmm, your findings do sound like it was the matrix leaking.

In mine the airbag ECU cover was missing and the ECU itself ended up full of green liquid - most likely why the airbag light was on!

My windscreen clears lovely now even with heat on. The heating also seems to be much more steady (used to be really hot or cold)…much improved.

Only issue now is the sunroof stated leaking/dripping so suspect the massive amounts of condensation was partially the matrix but also the sunroof it seems….roll on summer!

Yes, the temptation to start inspecting the seal is definitely worth resisting until you get at least one whole dry day!

When my blowers are on anything bold cold, there's an awful smell of antifreeze. Is that likely to be the heater matrix?

Doesn’t the air con evaporator have a drain to the outside world somewhere, could this be blocked? Assuming you have air con?

Certainly possible. A failing matrix, or seals, is not uncommon with coupes of this age.
Feel the carpet in the front footwells near the middle to see if oily residue comes off in your hand.

Also your windscreen will be difficult to clean inside as a greasy film builds up.

Robcal, mine started to mist up all the time and then it became impossible to clear the screen with any heat on and then even the air con wouldn't clear it.

There was a bit of a damp patch on the carpet piece that sits over the airbag ecu (yellow cable sticking out behind the stereo) but inspection of the removed matrix showed no obvious leaks/corrosion!!

I'm guessing they must fail inside and just a tiny leak will mean moisture (and antifreeze) is blown onto the screen no matter what setting the heating is on.

If there is a greasy film on the lower part of the screen then probably its the matrix.
Also if there is that 'hot radiator' smell then that points to the mtrix too.

Mine clears lovely now in about 5mins but due to a leak in the sunroof the condensation is back in the morning....

The matrix was less than £30 online I think (but you need seals) and it took me 3 hours to fit with most of that time trying to get the steering brace out!! A fiddle if your a big bloke I can imagine, and lots of lying on your back with peddles in your face!! The 'how to' was perfect!!

Bit of a random bump here, but is the matrix linked in anyway to the engine's cooling system? Just wondering if it would be worth getting it done at the same time as the radiator is being replaced.

Absolutely linked, it's actually part of the cooling system. Effectively a second radiator. That's why people will tell you to put the heating on in traffic if your engine starts to get too hot.

Getting the rad and matrix done together isn't absolutely necessary as coolant is relatively cheap so you could do one then the other later. That said, given the age of the coupe, it could be worth considering as piece of mind.

Unless you are getting a haze on the inside of the screen which is hard to wipe off, or a dampish stickyish patch in the footwell underneath the matrix it's probably fine.

It's not the sort of connection between matrix and rad as you might make for example between front spring and top mount.