W220 No heat from heater

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design guru

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Joined
Feb 28, 2004
Messages
486
Location
Hampshire
Car
2001 W220 Mercedes S320cdi & 2001 W208 CLK230K (SORN since 2008)
Hello,

It that time of year when the cold weather arrives and windscreens get frosted and just like clockwork my heating has decided to stop. All bloody summer it blew hot air.

Its a W220 S320cdi 2001 and I would usually link this to the thermostat but the car temperature sits nicely in 85, but the heater is only blowing cold air even when the heater is set to high/maximum. Could the thermostat still be faulty when inside gauge is showing the correct reading and cause this problem?

The other thing I noticed is when I pulled up and switched the car off I pressed the REST button hoping the heat would kick in but still only cold air.

Am I looking at the Duo valve as the main culprit in this situation?

I did loosed some coolant when the 3 way heater hose had a crack and i replaced it but would a loss of anti freeze cause the heating to stop?

Any help would be great, my heated seats are working on overtime at the moment.
 
Hi,
The Heater valve if it fails it is meant to fail in the "Hot" position eg. Warm air all the time.
With this in mind I think you're heater issue is a little more involved, something wrong with what controls the heater valve.
You should be able to just unplug the heater valve and it should make the heater hot.
If the heater goes to hot when the valve is disconnected then it is the Heater control that is at fault.
If unplugging the valve makes no difference to the heater temperature then the valve is at fault.
 
Hi,
The Heater valve if it fails it is meant to fail in the "Hot" position eg. Warm air all the time.
With this in mind I think you're heater issue is a little more involved, something wrong with what controls the heater valve.
You should be able to just unplug the heater valve and it should make the heater hot.
If the heater goes to hot when the valve is disconnected then it is the Heater control that is at fault.
If unplugging the valve makes no difference to the heater temperature then the valve is at fault.

Mine failed in the cold position.
 
Hi,
The Heater valve if it fails it is meant to fail in the "Hot" position eg. Warm air all the time.
With this in mind I think you're heater issue is a little more involved, something wrong with what controls the heater valve.
You should be able to just unplug the heater valve and it should make the heater hot.
If the heater goes to hot when the valve is disconnected then it is the Heater control that is at fault.
If unplugging the valve makes no difference to the heater temperature then the valve is at fault.
Is there a fuse that can be removed to disable the Heater valve or is it a case of removing all the wiper arms and housing to gain access?
 
Mine failed in the cold position.

It could just be that you're valve was jammed, and the electrical side of it still operated.
I should of said I am recalling something I read years ago regarding the heater valve, and in the case of my C Class AMG it proved to be correct, the article I read wasn't specific to the class of MB it was referring to just that it was the common behaviour of the valve.

Is there a fuse that can be removed to disable the Heater valve or is it a case of removing all the wiper arms and housing to gain access.

I don't believe there will be one specific fuse to pull to disable the valve, without disabling other functions of the car, with what I have suggested above it might also be worthwhile tapping the valve to potentially free it but if you cant get to the valve tapping probably wont be practical either.
Due to the potential difficulties in accessing it might be worth getting it plugged into STAR and see if there is any fault codes associated with the heater system, might save you time in the long term.
I see you are Hampshire, if you are in travelling distance from Southampton I can plug it in for you if you wanted.
 
It could be your heater control valve looks like the one pulled out of my car a while ago:eek:
hcj4K00.jpg
 
Mines on 230k so it’s probably due a change, got a used one online for £30. Do a full coolant flush while I’m replacing it, just need to source some decent coolant from MB. Will post an update on the result either way, thanks everyone for the feedback and input. Thanks for the offer Andy, I’ll get in touch if I have no luck. I did switch on the aux heater button next to the gear stick and it trickled some warm air for a while.
 
Mines on 230k so it’s probably due a change, got a used one online for £30. Do a full coolant flush while I’m replacing it, just need to source some decent coolant from MB. Will post an update on the result either way, thanks everyone for the feedback and input. Thanks for the offer Andy, I’ll get in touch if I have no luck. I did switch on the aux heater button next to the gear stick and it trickled some warm air for a while.

The valve is £25 new
 
Well after getting a Valve for the second time after finding out the first was the 00 84 design and I needed the 01 84 which has an extra inlet/outlet pipe hopefully I can get it fitted, it only took 20 minutes to remove the wipers, windscreen housing and wiper motor support last time so it should be a quick replacement fingers crossed. The clips holding on the pipes look like a pain as they are very closely bunched.

I few month back I had a random knocking sound from the dashboard and after replacing the 3 way heater hose as it was leaking and it stopped but it was only temporary as its started agin and after reading various threads I am thinking its one of the stepper motors. Its very odd as the sound only happened when I took a left turn over 50mph at first but now it just randomly knocks but again only when I am turning or veering left.

I have a telescopic camera so hopefully I can remove the comand and get a good look in there over the weekend, does anyone know if the error would show up on an icarsoft MBII V2 scanner?

I was getting random heat now and then but its only been trickling but it stops after 10 minutes, again this happens at random times.
 
Well I finally got around to doing the job, change the duo valve and flush the coolant. I am happy to say the valve made the difference, glad I read peoples threads as marking the pipes and where they go made it easier to ensure the correct pipes went back to the correct hose. It was a tight fit getting to the clips but removing the wiper housing made it 10 times easier.

Flushing the system made a big difference as the dirt in the pipes was quite bad. I would recommend a coolant flush added a few days before flushing as it seems to give the pipes a good clean.

Hot air and just in time as they are taking about a cold week ahead.

Only job left is finding the stepper motor causing the knocking behind the dash, if it is the stepper motor. It only happens when bearing left at certain speeds but recently it has done it at random moments.
 
Hi all, Driving back from Wales the other day, I started hearing a faint intermittent ringing noise and then realised the heater was blowing cold. I immediately read the engine temp and that was normal. I pulled over and checked the coolant level - ok.
With the engine stopped, I ran the heater fan up to full speed and back and that was normal. With the fan running, I cycled the flap positions and they too seemed normal.
The faint ringing noise, which persists. suggests to me that the coolant pump could be on its way. Anybody had this problem ?
A friend suggested that it may be a heater duo/mono valve gummed up. Do these W203 2.2 cdi s have one ? and if so where is it?
611 engine, 146K miles
 
Update, I was about to order a Febi water pump, idler pulley, tensioner pulley and belt when SWMBO walked in and said " Heater`s working fine"

Don`t ask me.!!!
 

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