These clips are tricky to remove. The plastic rectangles housing the wire clips are part of the U-pipe. Bear this in mind when detaching the U-pipe from the two other (pump and boiler) pipes - which have cone shaped flanges; easy to push U-pipe faces onto, hard to detach.

Using the perspective of Photo1 for reference, for ease of working, ensure the background is down towards the floor, and ensure the metal pipe is braced, directly or via the boiler resting on a non-slip surface like a rubber mat or carpeted floor. Set-up the equivalent if working from the pump end of the U-pipe.

Push a 2.5mm thick pointed tool (rod or flat) into the wire loop that emerges from the centre-bottom of the plastic face. Do not make the loop emerge farther, but you can widen it <1mm with a suitable width screwdriver.

Left and right shoulders of the wire clip are to be pulled apart as far as the plastic face will allow. Start by inserting (and leaving in place) similar 2.5mm-3.5mm thick pointed/tapered tools between the outside edge of the plastic face and the exposed wire ends. Insert near each shoulder.

With the wire clip being held apart in three places, check that the wire in the centre of the plastic face is not still hugging the pipe but is just proud of the rim of the cone-flange. Another pointed tool may be needed to manipulate the rest of the wire over the edge of the cone-flange.

With the perspective of photo1 (or equivalent view from the pump), use a finger either side of the pipe to push the plastic face away from the boiler or away from the pump (towards the floor if positioned as advised earlier). The plastic face may need rocking during this process to manipulate any remaining wire over the last sub-mm of flange.

The joint should disconnect gracefully. If the joint does not disconnect, examine the centre hole of the plastic face again, checking where the wire is fouling the cone-flange. Reposition the three other pointed tools -previously left in place holding the wire apart- as necessary.

The 'O' ring each end of the plastic U-pipe will be easily accessible once the joint is apart. The inner diameter is approx 3mm. Outer diameter is approx 5mm ('O' ring is 1mm thick).