Hi all,

Started having an issue with my Mk3.5 Octy estate a couple of weeks ago. Drivers side air vents blows cold air, whilst passenger side still blows hot air as normal.

(The missus noticed whilst driving me home after a few beers and after adamantly disagreeing in my inebriated state, i miserably discovered she was right the morning after commuting in as Scotland got it's recent 1oC spat haha!)

After having a flick through a few posts on here and reddit, my guess would be a buggered heater matrix/core that's got clogged up (currently have a silikat stamped coolant reservoir, which i think is the double walled one, rather than the bag).

So far, have tried/checked:

Resetting air vent controllers multiple times - no joy

Whether it's a teabag/double walled silica setup reservoir - believe it to be the double walled

The inlet & outlet pipes to the heater matrix, both are very warm/hot to the touch, with no obvious difference in temperature between them.

So i guess my questions are:

Is there anything else i should check/try/investigate to try and trouble shoot the issue?

Am i right in assuming it would be best to change heater matrix & coolant reservoir & get the system flushed if taking to a garage?

Has anyone had this done (semi-)recently at a garage and could give an idea of price? (ideally at a local place, we have a fairly sensible guy round the corner)

I've scoped out attempting to replace the heater matrix myself. Given the value of a garage doing it to be up near a grand in previous posts and that the part is actually relatively cheap, with fairly easy access (that i've already managed), I was wondering how bad it is to do yourself? From video guides my biggest concern is draining/refilling the system. The actual matrix part change i think i could manage without any great issue, but don't have the diagnostic tool to command the system to open up valves etc... to properly refill the coolant afterwards. Nor a vacuum filler, but a pal with a compressor reckons its easy enough to get a cheap conversion kit to diy one apparently...

So, is it possible to:

Do the change without fully draining and replacing coolant, either plugging the pipes quickly or just carefully catching lost coolant and refilling that which is lost after

or

Easily refill the coolant once the system is fully drained and matrix changed, without a diagnostics tool (and ideally other kit)

It's not a major pressing issue currently as still getting enough hot air to eventually warm the car up, just a ballache and might as well get it fixed in winter as it'll probably fully go eventually. Away for the holidays so can't chat to our local garage right now. If it's not a bad price I'd happily just leave to them, but know it is likely not going to be a cheap one... (They are very reasonable and sound, usually taking the 'if it don't need it' we won't do it' approach. Half hoping if i spoke to them and brought it in with a new matrix, access to the matrix via the glovebox already sorted, I might get a decent price. But ofc know that wishful and probably dumb/cheeky thinking!)

Thanks in advance!

~Max :)

As i understand it, the blockage can be caused by the silica bag, casting sand or both. Mine is the same. I’m thinking 2 hose clamps on the bulkhead heater feed and return , swap header tank, flush with treatment, drain down, swap matrix, then refill with g12 evo.

1 hour ago, crispymorgan said:

As i...

Clamps at the bulkhead would be a great idea to limit carnage! Thinking engine bay or cabin side? (Can't remember if the metal piping that connects onto the matrix goes the whole way to bulkhead or not...).

What was your plan for flushing? The bodge it hose it through after a quick blast of heaters on to get system fully open? Or use diagnostics?

Same again for refill? This is the bit that's giving me hold up 😫

It is probably the flap motor that has failed. Common fault. If you get a code read done via ODBEleven or VCDS, then you should see the failed flap motor error message.

Its fairly easy to get to - a reasonably competent person can replace it in an hour (it's just fiddly).

I just fixed this issue on my Scout.

I used an endoscope to look at the flap motors (you might be able to squeeze around the pedals to see it, but it's just easier to use the tool) - for me, there were no issues, and they were moving around fine.

The coolant in my expansion tank was a brown, muddy/scummy colour - not the lovely pink it should be.

I then purchased:
1x New coolant tank without the silica bag - metalcaucho 03344 from Autodoc - you can use the old tank's lid
1x New heater matrix (double check part numbers before you buy, as there are a few different fitments)
1x 5L concentrate of G12evo (successor to the rubbish G13 coolant)

1x set of hose clamps (amtech 3 piece set)

5x 5L Distilled water

1x Bottle of coolant flush chemical

Tools I already had, which you may need to buy if you don't have:
Spanners, sockets, screwdrivers, big set of pliers, tin snips, torx bits, a 1 meter rubber hose with an internal diameter matching the outer diameter of the coolant return hose that feeds into the top of the expansion tank, a small victoria clamp to fit around the aforementioned hose, the garden hose connected to the tap (ideally with an adjustable and lockable sprayer on the end), a rubbish towel I don't mind ruining, plastic sheeting to go under the towel, a few buckets, and a tupperware container the wife hopefully won't notice going missing.

I started by warming the engine up to operating temp, you can do this by driving around or just idling.

Once at temperature, I disconnected the coolant return hose, put it into the rubber hose and secured the victoria clamp to prevent it from leaking - I then ran the rubber hose into a buckets, and let the engine run. The old coolant ran into the bucket, and I topped up the expansion tank with the garden hose, occasionally changing which bucket the hose emptied into so I could monitor the colour of the water coming out of the car.

Be aware that if the water level in the expansion tank falls below the sensor, the car will sound an error on the dashboard. You don't have to worry about this as long as there's always liquid above the feed hole at the bottom of the tank.
Once the worst of the discoloured water had stopped draining, I then reconnected the return hose to the tank and added the coolant flush - I let this run through for 20-30 mins.
Whilst the coolant flush is doing its thing, it's a good time to prepare the heater matrix for replacement by removing the glovebox, footwell vent, centre console side panels and heater matrix retaining clip. BodriG has a good video on this, along with the rest of the heater matrix replacement steps: https://youtu.be/oHfQ_27dDRM?si=Rnah_XBRDNAvrNV5

Once the coolant flush had done its thing, I reconnected the return hose to the rubber drain hose and continued draining the coolant into a bucket and topping up the coolant tank with tap water.

After the coolant had started to run clear again, I turned off the car and installed the new coolant tank and heater matrix.

Once I had replaced both items, I then continued the flushing process, except this time topping up the tank with distilled water. I kept 1 bottle of distilled water to the side for mixing with the coolant, and once I'd used up the fourth bottle of distilled water, I then used the coolant concentrate to top up the tank - using 4 litres from the 5 litre bottle.
Once I'd put 4 litres of coolant into the car, I reconnected the return hose to the coolant tank, reattached all hose fixings, and all was done!
I also poured the remaining distilled water into the remaining coolant concentrate, such that I now have a bottle of readymix coolant to top the car up if required (I used a bit of this readymix to top the tank up to its correct level after I reconnected the hoses)

Cleaned up all the mess I had made, and now my car's heating is lovely and toasty warm on both sides.

There are videos on YouTube which run through the processes as well.

Edited 23 December, 202523 Dec by SpaceWalrus
Accidentally posted whilst halfway through writing

2 hours ago, SpaceWalrus said:

I just fixed this issue on my Scout.

I used an endoscope to look at the flap motors (you might be able to squeeze around the pedals to see it, but it's just easier to use the tool) - for me, there were no issues, and they were moving around fine.

The coolant in my expansion tank was a brown, muddy/scummy colour - not the lovely pink it should be.

I then purchased:
1x New coolant tank without the silica bag - metalcaucho 03344 from Autodoc - you can use the old tank's lid
1x New heater matrix (double check part numbers before you buy, as there are a few different fitments)
1x 5L concentrate of G12evo (successor to the rubbish G13 coolant)

1x set of hose clamps (amtech 3 piece set)

5x 5L Distilled water

1x Bottle of coolant flush chemical

Tools I already had, which you may need to buy if you don't have:
Spanners, sockets, screwdrivers, big set of pliers, tin snips, torx bits, a 1 meter rubber hose with an internal diameter matching the outer diameter of the coolant return hose that feeds into the top of the expansion tank, a small victoria clamp to fit around the aforementioned hose, the garden hose connected to the tap (ideally with an adjustable and lockable sprayer on the end), a rubbish towel I don't mind ruining, plastic sheeting to go under the towel, a few buckets, and a tupperware container the wife hopefully won't notice going missing.

I started by warming the engine up to operating temp, you can do this by driving around or just idling.

Once at temperature, I disconnected the coolant return hose, put it into the rubber hose and secured the victoria clamp to prevent it from leaking - I then ran the rubber hose into a buckets, and let the engine run. The old coolant ran into the bucket, and I topped up the expansion tank with the garden hose, occasionally changing which bucket the hose emptied into so I could monitor the colour of the water coming out of the car.

Be aware that if the water level in the expansion tank falls below the sensor, the car will sound an error on the dashboard. You don't have to worry about this as long as there's always liquid above the feed hole at the bottom of the tank.
Once the worst of the discoloured water had stopped draining, I then reconnected the return hose to the tank and added the coolant flush - I let this run through for 20-30 mins.
Whilst the coolant flush is doing its thing, it's a good time to prepare the heater matrix for replacement by removing the glovebox, footwell vent, centre console side panels and heater matrix retaining clip. BodriG has a good video on this, along with the rest of the heater matrix replacement steps: https://youtu.be/oHfQ_27dDRM?si=Rnah_XBRDNAvrNV5

Once the coolant flush had done its thing, I reconnected the return hose to the rubber drain hose and continued draining the coolant into a bucket and topping up the coolant tank with tap water.

After the coolant had started to run clear again, I turned off the car and installed the new coolant tank and heater matrix.

Once I had replaced both items, I then continued the flushing process, except this time topping up the tank with distilled water. I kept 1 bottle of distilled water to the side for mixing with the coolant, and once I'd used up the fourth bottle of distilled water, I then used the coolant concentrate to top up the tank - using 4 litres from the 5 litre bottle.
Once I'd put 4 litres of coolant into the car, I reconnected the return hose to the coolant tank, reattached all hose fixings, and all was done!
I also poured the remaining distilled water into the remaining coolant concentrate, such that I now have a bottle of readymix coolant to top the car up if required (I used a bit of this readymix to top the tank up to its correct level after I reconnected the hoses)

Cleaned up all the mess I had made, and now my car's heating is lovely and toasty warm on both sides.

There are videos on YouTube which run through the processes as well.

Forgot to mention - the advantage of this is that you don't have to fully empty the system and pressure refill it - I haven't noticed any issues with coolant flow after doing this

Hi

Did the heater matrix a few months ago as the wifes was showing the same issue,it got cold and her solution as always was to borrow my Octavia leave me with the problem 😂

Anyway, this job looked intimidating if you see some YouTube videos.

When you see how you did yours it should give confidence.

I managed it fine but very slow as back is agony.

But with a little help it went well.

The car is now better than mine on the heating front 😂

Just stuck bonnet ATM (I have a post on)