E250d Estate - 2012 - Rear brake pipes changed. Now cannot get brake pressure back.

[Jonners2022]

My car is in a local independent. They changed front discs and pads, and also rear brake pipes that had corrosion and failed MOT.
Job has been done but they are struggling to get the right resistance / hardness of the brake pedal. Suggesting ABS block / pump may need to go to a specialist. Valve may be malfunctioning. Brakes were fine when taken in!
Any thoughts on what the problem could be. I would like to give them a steer if possible to try and eliminate 'trial and error' leading to more complex problems. I have read the forums and consideration should potentially be given to:
- Use of a pressure bleeding system needed
- Possible need to use MB Diagnostic system to bleed ABS pump
- Air or contaminants in Master Cylinder
- Traditional bleeding, by pumping pedal may have damaged Master Cylinder seals, now allowing bypass?
Any theories or help appreciated

 

[Cole@MBS]

Very common problem, we see this daily! Needs a pressure bleeder and old fashioned helper pumping the pedal at the same time, think we done two this week for other garages!!

 

[malcolm E53 AMG]

Welcome!

Might be worth removing the brake master cylinder and bleeding off the car air trapped in there can be an absolute pain to bleed can’t believe it can be anything else as the car was ok when it went in. When you say specialist garage I guess it’s a MB specialist?