Good morning first time i hsve posted dont know if anyone can help i have a 2018 ds7 crossback prestige the problem i have is passengers side heater working fine but drivers side is cold all the time any ideas what it could be thanks in anticipation Kevin
First, check the fuses in the BSI. If they’re OK, check the driver’s seat heating mats. If one is faulty, both won’t work.
Can the driver’s seat position be adjusted? Does the seat heater light turn on?
Hi Andrew yes drivers seat ok its the fan heater air coming through air grills hot on passengers side blowing hot drivers side blowing cold
Sorry, I read too fast and was thinking about heated seats.
Typically, your problem is caused by a clogged heater core or low coolant level.
Wouldn’t clogged or low level affect both sides? My guess is that its either a bad sensor or a defective flap that doesnt open when asked for.
No, first symptoms of clogged heater core are like that:
In newer models, the most common problem is a clogged heater core. The Peugeot 407 had a faulty control unit or broken flaps, and everyone keeps going back to it. Later, with the P508/DS5, heater core problems began and continue to this day.
Currently manufactured heaters have very narrow channels in which dirt easily accumulates.
You can read by Diagbox the flap and control data, but it’s probably fine.
Verifying the heater core is easy and cost-free. Simply compare the coolant temperature at the heater core inlet and outlet.
Thanks for that will have a pook.chck if its blocked
But - shouldnt a blocked core affect both sides? I’ve never read or cared about the issues with the old models. My suggestion was based on most semi modern cars 
Contamination of the heater core doesn’t completely block the fluid flow. Unfortunately, the fluid quickly loses temperature because there’s too little of it, one part of the heater core hot while the other part is cold from the cold air flowing through.
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