Mercedes W124 duo valve heater control valve auxiliary water pump Bosch A0018303784 0392020028
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Refurbished genuine duo valve with auxiliary water pump – like new. Bosch/Mercedes genuine part A0018303784 for the late W124: valve and integrated auxiliary water pump completely overhauled, all wear parts replaced, thoroughly cleaned – not an untested used part.
Valve and auxiliary water pump completely overhauled · Every valve individually tested · 5-year warranty
Leak tightness ✓Flow ✓Switching function ✓
Every valve is tested individually after refurbishment: 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.
♻ Old-part bonus: 35 € back for your old duo valve
Buy this valve at the regular price, install it at your leisure, and then send us your old duo valve with auxiliary water pump – even if it is defective, as long as it is complete. Upon receipt we will refund you 35 € to your payment method (15 € for an old valve without a pump). Simply send in the old part within 60 days on our buyback page – all conditions are listed there as well.
| 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) | completely overhauled, all wear parts replaced, tested three times | 5 years ✓ |
How can you tell a duo valve with auxiliary water pump is defective?
One side no longer heats, the heater stays hot permanently or fails completely – the cases vary and can affect one or both heating circuits. The duo valve sits in the engine bay on the bulkhead and, by pulsing, controls the heating water flow to both heater cores (side-independent temperature control, de-energized open = full heating output).
Typical for the version with auxiliary water pump: when stationary and at low engine speed the heater does not get properly warm, while it works at higher engine speed – then the pump no longer delivers enough heating water.
Detailed diagnostic instructions in the 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 Tempmatic
- 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 applies per piece. Scope of delivery: see product images.
⚠ 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 what counts, please compare 1:1. We also have the version without a pump in stock, refurbished: 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: +49 179 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 is a problem, simply send the valve in – we repair or replace it. In addition there is a 60-day return policy and free shipping within Germany.
How does it differ from the valve without a pump?
This version has an integrated electric auxiliary water pump that circulates the heating water when stationary and at low engine speed. It carries part number A0018303784 and was generally fitted from approx. 08/1991. The version without a pump (A0008306584) is not identical in construction.
How is the valve tested?
After refurbishment, every valve goes through our own in-house developed test procedure with three stations: leak test, flow test and switching test of both valve circuits. Only when all three are passed does the part go on sale.
Why is there no new part?
Mercedes no longer supplies this valve, and there is no aftermarket version on the market. That is why we fully refurbish genuine parts – “like new” condition.
KFZTeile-Thot specializes in spare parts for classic Mercedes cars. Every duo valve from our refurbishment program goes through our own in-house developed test and refurbishment procedure.
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