Cap on boiler pump

[Milleniumaire]

I have a Vaillant 637 system boiler, which has the newer Grunfoss pump. On the top of the pump towards the back is what looks like a grey tyre valve cap with a small hole. I'm assuming this is used for venting the pump?

I noticed a bubble of water coming out of it and white (limescale?) on the pump around it, so it appears to be leaking slightly. It can be twisted and was loose. I unscrewed it a little half expecting to see some water come out of the hole (like a radiator bleed valve), but nothing happened so I screwed it back to how it was (not quite as tight as it could get).

Does this indicate an issue with the pump? Should it be as tight as it can get?

Thanks.

 

[Phill Peck]

It should be loose

But you shouldn't have the front off that boiler

Why was the front removed?

 

[Milleniumaire]

Having had a conversation with my fitter he has explained this is the automatic vent for the pump and that it should be loose as you say. This wasn't actually the case; it was almost tight, but not quite, so obviously needs to be loosened up and then no doubt it will leak even more! Unfortunately, this is something else my fitter will need to replace.