When I tried to connect BC pipes to a GTCE boiler, steam doesn't all come out even if the capacity of the pipe is bigger than the steam production rate. There are no problems when putting a tank next to the boiler.

BuildCraft version: 7.99.17
Forge version: 14.23.4.2705
Singleplayer or multiplayer: SSP
Steps to reproduce:
1.Place a GTCE boiler
2.Add water and fuel
3.Place a pipe on whatever side of the boiler except bottom
4.(Optional) connect the pipe to a storage device just to ensure the pipe is not filled up
5.Wait until steam comes out
It should look like this:

Additional information: Please see GregTechCE/GregTech#225

The GTCE boiler is a block that will try to output steam on all sides except the bottom side, just FYI.
Also found the extraction pipe is not outputing. Might be the same bug.

pipes have a max throughput, stone is one of the lowest ones, did you try putting a gold one directly on top of the boiler? stone has one of the lowest transfer rates

and the extraction pipe is outputting to the gold one, the fact that the wooden one looks like it has more liquid is probably due to a difference in how much the wooden pipe can tranfer and how much the golden can handle, try using multiple wooden pipes leading to a golden pipeline?

tried with the gold pipe and same thing happens, pipe in the background

AEnterprise says:

the fact that the wooden one looks like it has more liquid is probably due to a difference in how much the wooden pipe can tranfer and how much the golden can handle

I used the wooden diamond fluid pipe as the extraction pipe, not the wooden pipe.

do you happen to know how much steam per tick the boiler generates?

Depends on the temperature. At lowest temperature, it generates 15mb/t. At highest temperature, it generates 30mb/t.
The same thing happens to the small bronze boiler, which produces 6-12mb steam/t.

if GT doesn't output every tick but every 5 that would explain why the pipe doesn't accept it all, also nothing we can really do from BC's end, you'll need multiple pipes or indeed a tank with multiple wooden extraction pipes

Might be related to how GT machines do not eject fluids every single tick, but instead eject once every 5 ticks. Since the boiler generates 150mb in that interval, but the BC pipe can only accept 80mb in a single tick, the GT boiler's auto eject behavior is not sufficient to push all of the steam through a BC pipe.

You'll need a powered extraction pipe.

if so, why does the golden pipe not filled up?

Because even though the gold and wood-diamond pipes have the same transfer rate in mb/t, the gold pipe also has a smaller transfer delay - the time between a fluid entering the pipe and the fluid being allowed to leave the pipe.

it's not just the delay, the pipe can accept fluid every tick, but it's not getting fluid ever tick, only every 5 ticks

and those every 5 ticks the machine tries to push more fluid into the pipe then the pipe can accept, so it only accepts part of the fluid and moves it throught the pipe

if the machine was pushing more then (or equal of) what the pipe can accept/transfer each tick it would fill up

AEnterprise says:

if the machine was pushing more then (or equal of) what the pipe can accept/transfer each tick it would fill up

so the pipe should fill up every 5 ticks, but it won't.

that's not how pipes work, a pipe accepts up to x amount of fluid per tick and starts moving through the different segments of the pipe, a pipe only fills up completely if it gets as much as it can transfer every tick