There is very little information out there regarding this issue with our GLS models. My cooling system is working fine - radiator is full, no leaks, no air, all good. However, when I set my thermostat to call for heat, I get fan output from all vents that are selected but I get no heat. I have read where earlier models of the GL's and S500's and others have a "heater control valve" back by the firewall that has a solenoid that when heat is selected it enables the flow of hot coolant through the heater coil to provide heat. On these models it is a part that appears to be between $100 and $150 and once you get to it - appears to be easy to replace.

I went to my dealer today to buy the part so that I would have it in hand while I pull apart the panels around the wipers and top of the firewall area behind the motor, however they were not able to find the part listed in their system and are telling me that there is no such heater control valve. Not sure I am buying this since they were only not able to find the part vs. being knowledgeable about the system in the car. They recommended that I tear into the car and come back with the part so they can match it up. However, their service department told me that they can fix it with some other $60 part and $1,350 in labor at $250 per hour. Quick math tells me they believe this is a 5.4 hour job.

Needless to say, I am hoping someone on this forum has run into this issue and can steer me in the proper direction. Anyone else run into this "no heat" issue and if so what was your fix?

I have found several videos where people overwhelming found that it was this solenoid operated 3 or 4 way valve on both S500's and E Series - behind the engine and a small access panel near the firewall. Am hoping it is this easy so I can do it myself in an hour or two. Thanks in advance for any assistance here!

 

Hoping to get some help on this one - am at a loss ... anyone have this "no heat issue" but everything appears to be working well?

 

Hi
i just signed up to respond to this.

i have a 2017 gls 550 at about 110k km. starting this winter, the car started to have no to very little heat :
1. engine temp is ok
2. at very low fan speed i can feel the warm air but as soon as i turn the speed high, air becomes cool as it seems that the heat cannot keep up with the higher fan speed.
3. coolant level is okay.
4. fan is working fine.
5. ac works fine last summer.

i brought the car to 2 reputable indy shops in my city. the 1st shop told me that computer returns no faulty codes and based on his diagnosis, everything seems fine. based on his experience, he said it could be engine head gasket leak which would be an expensive job to repair. the shop basically says there is not much they can do and would recommend me to get rid of the car when the weather gets warm. lol, at least they are being honest and i will give them that.

then i brought the car to the 2nd indy shop and after 2 hours of diagnosis, they are not exactly sure what the issue is but suspect that it could be a water pump issue. the rationale is that it seems that when giving gas, it gets a bit of more heat. again, computer scan returns no faulty codes, which aligns with first shop. i am not every mechanically inclined so i basically took a leap of faith and decided to get the water pump replaced. the car is still in the shop. if they cannot fix the issue by replacing the water pump, i probably will seriously think about getting rid of the car.

base on my experience with these 2 shops, i think if i bring the car to the dealer, they probably would recommend me to change everything like heater core water pump etc. i heard that replacing the heater core is a 12 hour job and i am not sure if i am ready for that expense.

none of the shops mentioned heater valve.

i will let you know if replacing the water pump fix the issue.

 

My 2017 GLS550 with 91,000 miles just spent 2 months at the dealer for the exact same no heat issue. They said something in the heater core burst like the silica gel packets and affected a bunch of stuff they replaced the heater core, radiator and other things. Bill was like $10,000 with $7000 of it being labor. I was a few days outside of CPO warranty and dealer was able to get MB to cover it.

 

Why in the hell would there be silica gel packets in the radiator. The thing is made to hold water.

 

The silica gel bag in a Mercedes coolant jug helps maintain the level of silicate protection in the coolant. The bag is built into the jug and is a permanent part of the car.

above is what i found online. seems like common issue based on my research..

 

Wow, learn something new every day. There is no way the amount they put in there could clog a radiator or, at least, it doesn't make sense that they would put enough in there to clog one.

 

yeah if you google mercedes heat issue, it seems that some people are experiencing the silica gel issue. Thorough coolant flush might get them out and fix the issue. But dealer being dealer, they would just replace everything.

 

Maybe you can reverse flush the heater core.

It may be possible to plumb a filter in line with the heater core as a preventive measure. This one is 600 microns (0.02"). Should be enough to prevent clogging.

 

just an update on this: so i got the car back after water pump and some hoses were replaced. The shop also did multiple coolant flushes and i was told that they didnt see anything. While it was warmer than before we are also experiencing a cold snap here in southern ontario.
i am still not 100% convinced that the water pump is the issue. Will see if this is still an issue after a few days.

 

an update...the water pump replacement didn't do much to the heat....

just had another shop replace the coolant bottle and flush out the heater core really well....the heat is now back on before the winter!

 

Thanks for the update - so it sounds like the flush fixed the issue, however if you replaced the coolant bottle with a new silicate bag that comes with it ... are you concerned that it may happen again? Im wondering if I should just have my heater core and other components flushed and keep the current coolant bottle. Thoughts?

 

that is a good and valid concern. It might happen again 5-7 years down the road if i am on the wrong side of the statistics. If i still have the car at the time, i guess i will deal with it again.

 

I had a similar issue with our 2019 GLS550 about a month after purchasing it as a certified used vehicle back in Fall 2022. I actually came across the concept of the silica in the cooling system from this forum. The service advisor complex blew it off, almost scoffing at it, saying Mercedes doesn’t do that. I just kind of ignored it and let them diagnose the issue since it was under warranty. After multiple failed repairs, they said they were flying in a Mercedes Engineer to help diagnose the issue. This was after about 3 months of them trying to resolve the issue. They then said it was repaired and that the heat was consistent. When I went in to pick up the vehicle they told me silica had gotten into the system (the same advisor that told me that Mercedes doesn’t have that). I wasn’t very happy since I had been driving a loaner for 4 out the 5 months I owned the vehicle.

Fast forward to today and the wife is telling me the heat is intermittent. One start it works, the next time it doesn’t. Coolant looks pretty full and I haven’t seen leaks, but the coolant is kind of dark. Hoping it’s not a head gasket, but I might do a test on the coolant bottle to rule that out.

 

i am no expert but the head gasket issue should have nothing to do with intermittent heat if coolant level is stable. What is your engine temp when it fully warms up?

 

I say stable, but it seems it’s a little low. I added about a 500mL today. Just want to rule out the head gasket. It’s unlikely that there’s a bad one, but want to check it off the list.

 

if you had to add 500ml, i think it is low. however, after coolant flushes, from my experience, it is typical to top up 500-1000ml later. but if you have to do it constantly for a few months, then it is a problem..

 

update?

Coolant bottle or head gasket?

 

I have a 2018 GLS550 with 117k miles. Getting very little heat in the cabin (has rear climate control). Engine temp is stable. Pressure tested at 14 psig and held constant after 30 min, so I don't think it is leaking. Had to replace all of the $%$^$ plastic coolant lines to/from the turbos. Wondering if there is air trapped in the heater core. Haven't really used the heat until recently. Any suggestions on diagnosis/remedy?

 

worth a try if you can find an indy shop to do a heater core flush and have the coolant reservoir replaced...i just did mine on my 2017 gls550 and it improves a lot though still not back to 100% where it used to be..where i am in Canada, the heating is now okay if temp is above -10 C but when it gets to -20 range, it struggles to keep up...the consensus is that silica bag in coolant tank leaks and plug up the core....i think the dealer would ask you to replace the heater core which is very time consuming and costly...