Mercedes W124 duo valve heater control valve auxiliary water pump Bosch A0018303784 0392020028
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Refurbished original duo valve with auxiliary water pump – like new. Bosch/Mercedes genuine part A0018303784 for the late W124: valve and integrated auxiliary water pump fully overhauled, all wear parts renewed, thoroughly cleaned – not an untested used part.
Valve and auxiliary water pump completely overhauled · Each valve individually tested · 5-year warranty
Leak-tightness ✓Flow rate ✓Switching function ✓
After refurbishment, every valve is individually tested: leak test, flow test and switching test of both valve circuits.
5-year warranty on this refurbished part
Should a problem occur: send in the valve – we will repair or replace it. In addition, a 60-day return policy and free shipping within Germany apply.
| Your options | Condition | Warranty |
|---|---|---|
| Mercedes new part | no longer available | – |
| Untested used part | Condition of valve and pump unknown | none |
| Refurbished genuine part (this listing) | fully overhauled, all wear parts renewed, triple-tested | 5 years ✓ |
How can you tell if a duo valve with auxiliary water pump is faulty?
One side stops heating, the heater stays permanently hot, or it fails completely – the symptoms vary and can affect one or both heating circuits. The duo valve sits in the engine bay on the bulkhead and pulses the heater water flow to both heat exchangers (side-separated temperature control, de-energized open = full heating output).
Typical for the version with auxiliary water pump: at idle and low rpm the heater doesn't get properly warm, while it works at higher rpm – then the pump no longer delivers enough heater water.
Detailed diagnostic guide in our guide: W124 heater cold at idle? Check the auxiliary water pump on the duo valve
Fits the following Mercedes models
Model series 124 with automatic climate control or Tempmatik
- W124 sedan
- S124 T-model
- C124 coupe
- A124 Cabriolet
This version with integrated auxiliary water pump was generally fitted from approx. 08/1991. Vehicles with manual heating (Bowden cable) do not use this valve.
Part numbers: A0018303784 / 0018303784 (Mercedes) · 0392020028 (Bosch). Price is per piece. Scope of delivery: see product photos.
⚠ Important: compare the part number before buying
The version without auxiliary water pump carries the number A0008306584 and is a different part – as are other deviating numbers. The number on your installed valve is decisive, please compare 1:1. We also have the version without pump refurbished in stock: Duo valve A0008306584 without auxiliary water pump.
Does this part fit your car? Send us the VIN (chassis number) and model year – we'll check it for free: 0179 8991069 (Mon–Fri 8 am–6 pm) or via our contact form.
FAQ
What warranty is provided?
5-year warranty on this refurbished part. If there's a problem, simply send the valve back to us – we'll repair or replace it. Plus a 60-day return policy and free shipping within Germany.
How does it differ from the valve without pump?
This version has an integrated electric auxiliary water pump that circulates the heater water at idle and low rpm. It carries the part number A0018303784 and was generally fitted from approx. 08/1991. The version without pump (A0008306584) is not interchangeable.
How is the valve tested?
After refurbishment, every valve goes through our own, in-house developed test procedure with three stages: leak test, flow test and switching test of both valve circuits. The part only goes on sale once it has passed all three.
Why is there no new part?
Mercedes no longer supplies this valve, and there is no aftermarket version on the market. That's why we fully refurbish genuine parts – condition "like new".
KFZTeile-Thot is specialized in spare parts for classic Mercedes. Every duo valve from our refurbishment program goes through our own, self-developed testing and refurbishment process.
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