Boiler does not fit in the niche. What options are there?

Hello. Our installer delivered a different boiler than originally planned. His reasoning is that otherwise the BAFA subsidy would not be met. The small boiler above in the niche was also added as a result.

Unfortunately, the boiler no longer fits in the niche. However, this niche was not originally intended for the heating system anyway. The connections on the boiler are at the back. The boiler is exactly as wide as the niche. So, the plumber cannot secure the pipes first and then place the boiler into the niche. The pipes also cannot pass alongside the boiler because both are the same width.

What can we do? Aren't there flexible connections that can be screwed on first and then the boiler pushed halfway into the niche? Do you have any other ideas? The plumber suggests the spot where it is currently standing.

would put shelves there

I would also leave it there and put shelves up. You can do it with the flexible cables, but it's better if you can get everywhere without having to move half a ton of tank.

The problem is that a sink is also supposed to go on the right wall. You can barely get through between the boiler and the sink. The space in the niche and to the right of the boiler is therefore pretty much wasted?

I just spoke again with our installer. He says it would work with flexible hoses, but they quickly become leaky and clog up fast. Can you confirm that?
We want to call again at half past ten.

Edit: Isn't a water tank for an air-to-water heat pump quite large anyway?

Chisel open the wall and lay the cables inside, then connect them at the front?

Unfortunately, the boiler no longer fits in the niche. However, this was not originally intended for the heating system anyway.

Or revive the original plan?