How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • Go back-and-forth until satisfied
    Rate the answer you receive.
Ask CarDoc Your Own Question
CarDoc, Auto Mechanic
Category: Car
Satisfied Customers: 417
Experience:  IMI L3 Motor Vehicle Mechanic
Type Your Car Question Here...
CarDoc is online now

I can't get hot air, the coolant level is ok and fan works

Customer Question

I can't get hot air, the coolant level is ok and fan works well. Have two diagonsis, but the garages couldn't find out what the problem is. May you help me?
JA: Have you checked the coolant level? Have you checked the hoses for leaks?
Customer: Coolant level is OK, but have no idea about the hoses. my previous owner said to me that he replaced the heater hose by himself with Mercedes part.
JA: What is the model/year of your Mercedes?
Customer: C250, 2010
JA: Are you fixing your C250 yourself? What have you tried so far?
Customer: No, my previous owner replaced the heater core like 1 year ago?
JA: Anything else you want the Mechanic to know before I connect you?
Customer: no, that's all I have.
Submitted: 3 months ago.
Category: Car
Customer: replied 3 months ago.
probably 1 year ago, my previous owner had changed the heater hose and O ring.
Customer: replied 3 months ago.
It just happened 3 weeks ago, and it's wired because sometimes I could get proper hot air, but most of time I couldn't.
Customer: replied 3 months ago.
I am sorry, my previous owner didn't replace heat core, but heater hose. I am sorry.
Expert:  CarDoc replied 3 months ago.

Thank you for using JA. I'm Baz, one of the automotive experts, I try to be available in the afternoon on weekdays and in the evenings on the weekend. I apologise if I do not respond to your question promptly, I can assure you that I will respond as soon as I can. Thank you


Expert:  CarDoc replied 3 months ago.

Have you connected a diagnostic tool to the car to check live data? Is your engine temperature gauge getting to the optimum level?



There are various temperature sensors which can go bad due to dust/dirt build-up also, if you have an auxillary pump (found on the side of the coolant tank), this can also go bad which stops the coolant from flowing to the radiator used for the cabin heater.

Customer: replied 3 months ago.
1 week ago, I called a electrician to have diagnosis, but he said no error. The temperature gauge works fine, the fans work good.
Expert:  CarDoc replied 3 months ago.

Ignore the call request.


Do you have an auxillary pump attached next to the coolant tank? (please see pic) The heater system also has temp sensors in all the vents and also a temp sensor outside, any of these going bad can affect the heat going into the cabin.

Have you tried taking it to another garage? This is not a simple diagnosis, it's quite complicated.

Customer: replied 3 months ago.
Hello. I've recently changed the headlight bulb because I thought it's a bit darker. unfortunately, it didn't work. I mean the light is still dark. I think there are some condensation on the outer plastic of the lighter, and it makes the light darker. Is there any quick solution about this?
Expert:  CarDoc replied 3 months ago.

Condensation occurs due to the headlight not being sealed properly, the head light is supposed to be sealed unit, that's why the caps for the bulb covers have air tight seals.

There are a few ways in which this air tight seal can be compromised; this can happen at the back of the head light (where you replace the bulbs) or where the 2 parts of the head light are joined, the seal that joins the 2 headlight sections, can wear/deteriorate which can allow moisture to enter. Also, look for cracks, you will have to remove the head light to inspect closely.