Fuel filter change – priming bulb (hand pump) not building pressure, stays soft

[habo]

Hi everyone,
I recently changed the fuel filter on my C4 Grand Picasso with the 1.6 HDi 9HZ (DV6TED4) engine.
When I tried to prime the system using the rubber hand pump (the priming bulb above the engine), I pressed it around 500 times but it never sent any fuel to the filter.

I disconnected and reconnected both fuel lines on the filter, but nothing changed.
Eventually I removed the filter, filled it with diesel manually, reinstalled it, and the engine started on the third crank.
I let it idle for about 30 minutes and it ran fine.

However, the priming bulb stays completely soft whether the engine is running or stopped.
It never gets firm, as if it's building pressure or pulling fuel. Is this normal?

What worries me is why it didn’t send any diesel to the filter while priming.
The car sat for two days afterwards and started immediately, so it seems to be running normally now.

I spoke with a Citroën mechanic and he told me not to worry, but since I’ll be going on a long trip soon, I’m still concerned.
Because the priming bulb sits in the engine bay, I’m wondering if over the years it may have developed tiny cracks and is sucking air instead of diesel when pressed — or if the non-return valve inside it (or somewhere in the line) may have failed.

The part in question is 1574 T5.

Any advice or experience with this issue would be appreciated.

[mickthemaverick]

I have come across a bulb with a blocked inlet before but that's the best I can offer

[MattBLancs]

Is any of the piping clear (potentially covered with a braided black outer plastic that can slide along the clear tubing) if might able to see a stream of constant bulbs going past. If starting normally then seems like it's not too happy.

[Gibbo2286]

I would be looking very closely for cracks/pin holes in the bulb.

[Paul-R]

I had to replace the primer bulb on my daughter's Vauxhall Vivaro because the non-return valve inside stopped working.

[Steve Walsh]

Changed a fuel filter on a 1.6 hdi Berlingo at weekend, Primer would not pull fuel and go hard, I used a Vacuum pump on fuel line and after the engine had run primer bulb worked fine, Maybee valves get dry and wont pump