Heater not getting hot

[Redwolf]

Hi. Looking for some advice regarding an issue with my daughter in laws car. I have trawled forums and YouTube but struggle to find anything specific for this particular model or issue. Apologies if this has been covered but I can’t find it.

The Car: 2017 Audi A4 Diesel Avant Quattro (B9), engine - DETA

The problem: She complained that the cabin never gets hot and she is freezing by the time she gets to work. I have sat in the car when she has returned from work, with the temp set to 28C, and can confirm it is cold in there and that the heater does blow out ‘warm’ (not hot) air at the ‘face/centre level vents’ with the temp set to 28C. Feeling down at foot level and in the rear they are blowing cold.

My initial thoughts were maybe there was insufficient hot water and that the heater matrix was blocked and need to be flushed, I also wondered if there was an issue with the flaps/gates not opening that control the flow through the ducts.

Here are some of the checks/tests I have already done and any outcome.

·        Is the heater matrix blocked? When the car engine was hot (90C) I felt the flow and return pipes that go from the engine bay to the heater matrix. I could tell no difference in temperature; they were both hot. My conclusion is matrix is probably OK. (This car does not have those silica bags in the coolant bottle to clog the matrix)

·        Are the flaps opening? If I turn the temperature down at about 18C I could hear a motor behind the dash and the air flow went cold, when put back higher, I again heard a noise and temperature got warmer. Could also hear motor when selecting different settings (demister or feet). Tested the same for the passenger side. My conclusion is that the ‘flaps/gates’ are working OK

From the above tests my thoughts are that there are probably no blockages in the matrix and that the control units are working correctly. I am now thinking that although the flow and return pipes to the matrix are hot and we do get warm air, that the coolant isn’t actually hot enough.

The car temperature gauge never exceeds 90C. I then felt the main radiator hoses. The top hose was hot (not boiling hot), but the bottom hose was stone cold!

My thoughts now are it could be a faulty thermostat. So here is the next problem, thinking this might be a relatively ease thing to swap out I cannot find any information (forums/YouTube) of where to locate and change the thermostat on this model.

She did mention that even on the coldest of days (0C) the car doesn’t get above 90C but the radiator fan will be on.

Is the thermostat housed within the water pump or a separate housing?

Where is it physically located?

If in the water pump is that part of the cambelt assembly?

If you got this far reading my ramblings, then well done and thank you! If you can offer any advice and guidance, point me to some ‘how to’s” (for this particular engine) then that would be much appreciated.

Thanks for reading.

Regards, Kevin

[Steve Q]

I'd recommend a diagnostic check to see if any fault codes flag up. 

Could be an issue with the heater matrix or with the heaters temp sensor etc. 

Also is the engine temperature normal (90 degrees). If not could the thermostat be failing? 

[Redwolf]

Thanks Steve. I have VCDS and nothing came up on there. I believe 90 degrees is the norm though I was surprised that the bottom hose was cold even after a long run.  

[ian.f]

Hi,

Apologies, I can’t offer a solution (yet), but I have the exact same issue. You could actually be driving my car!!

I’m currently mid-way through a heater core flush but ran out of time yesterday. Finishing it later today. 
 

Hopefully this’ll do the trick and I can report good news later, but I’d like to follow this chat in case it didn’t. 
 

🤞

[ian.f]

3 hours ago, ian.f said:

Hi,

Apologies, I can’t offer a solution (yet), but I have the exact same issue. You could actually be driving my car!!

I’m currently mid-way through a heater core flush but ran out of time yesterday. Finishing it later today. 
 

Hopefully this’ll do the trick and I can report good news later, but I’d like to follow this chat in case it didn’t. 
 

🤞

Ok, flush completed. No difference. Heat in cabin is luke warm at best. 
 

So keen to hear any ideas on this one!

[alpha omega]

hi,i have an audi a4 avant tdi but mines the b8 and i see your d/i/l's is a b9....hope her thermostat is not in the same place as mine as its a pain to do(see pics)mine is the thermostat(circled pic 1) surrounded by the casing it comes complete.i had to remove the alternator(pic 2 expanded view) to get to the torx screws and to be able to manoeuvre the thermostat and casing out....what a job getting it out,and back in.i had to put a clamp on the pipe to the right of the thermostat(see pic 3) to stop a leak i got after putting it all back together Grrrrrrrrrr.lol.....good luck hope your d/i/ls is easier to do than mine was.i only changed the thermostat as a precaution as i had changed the cambelt aux belt and rollers and because of the high mileage.kind regards stephen

[Redwolf]

Thanks for the info Ian, I am reluctant to flush as I am not convinced the matrix is blocked. My current thoughts are a) The coolant is just not hot enough, hence thinking about the thermostat, and b) I can here the motors that move the heating flaps in the ducts but are they actually move full distance. Before I pull the car to bits I have a cheap (Aldi) endoscope, so I am going to see if I can feed under the dash and actually see any movement. Will update if/when I find anything

Cheers Stephen. I was hoping the Thermostat wouldn't be too bad to get at, but it sounds horrendous. The car is due a service and cambelt, so seems an appropriate time to do the the Thermostat as well!

[alpha omega]

your welcome kevin.

[Magnet]

Hello Kevin,

What is the coolant temperature gauge reading after a few miles of running?

Kind regards,

Gareth.

[Redwolf]

Hi Gareth.

It hits 90C and never goes above.

[Stevey Y]

12 minutes ago, Redwolf said:

Hi Gareth.

It hits 90C and never goes above.

Hi there are two thermostats one on the water pump which is prone to sticking open, if its a cn engine and has the solid inlet manifold the other thermostat is under that that one controls the cabin heat and you can change it without removing the manifold just buy a new core unit and seal, I did mine on my A6 similar engine it fiddly but doable, also posted pics of parts and how to in the A6 C7 part of the forum.

Steve.

[ian.f]

On 1/31/2024 at 2:07 PM, Redwolf said:

Thanks for the info Ian, I am reluctant to flush as I am not convinced the matrix is blocked. My current thoughts are a) The coolant is just not hot enough, hence thinking about the thermostat, and b) I can here the motors that move the heating flaps in the ducts but are they actually move full distance. Before I pull the car to bits I have a cheap (Aldi) endoscope, so I am going to see if I can feed under the dash and actually see any movement. Will update if/when I find anything

Cheers Stephen. I was hoping the Thermostat wouldn't be too bad to get at, but it sounds horrendous. The car is due a service and cambelt, so seems an appropriate time to do the the Thermostat as well!

No problem. 
Just a little update, post flush. We’re away this weekend, so have put 150mi solid drive since the flush. 
 

The car is now much hotter. Still nowhere near where my wife’s GLA gets, but I wasn’t cold on the drive. 
 

@Redwolf do you have Carista by chance? I do, and found a HVAC calibration which checked and set all the flaps on the vents. That would (I think) throw an error is any we’re stuck.  Don’t know if that helps or not. 

[Redwolf]

No dont have Carista, just have Ross Tech VCDS which I would have thought might do the same thing. Thanks for the update on the flush.

[ian.f]

16 hours ago, Redwolf said:

No dont have Carista, just have Ross Tech VCDS which I would have thought might do the same thing. Thanks for the update on the flush.

Yeah I’d assume it’d have a similar function. Defo worth a look 👍👍