Worcester 24i Junior making funny noises

[Peadee]

This is my first post here and I am really hoping that it provides me with the answers that I am looking for
I have not needed to use my central heating for at least the last 4/6 weeks due to the weather being almost summerlike
So, the other day I thought I had better run it for half an hour or so. Just to make sure that it was ok. It was, for about 90 seconds. It started to make some awful noises and then started to knock and bang. This was closely followed by a hissing sound just at the point that I decided I should turn it off. I tried it again 5 minutes later and it ran ok. The following day I once again turned on the CH and again the noises came and have done each time since.
I thought I may have an airlock in the system so I turned off the boiler and drained the whole thing and then refilled it but this had no effect so clearly there was no airlock.
I then removed the front panel and ran it to see if I could see what was happening. As i looked in from the front it became clear where the hissing sound was coming from. Just behind and above the pump there is a black cap and it looked as though atomised water was escaping from it. It could have been steam but it looked more like water being forced through a very small hole and atomising.
I have looked in my installation and servicing instructions and I believe this part is called the "air vent cartridge". Am I correct and if so, am I ok to go ahead and buy a new one and replace it and where do I get one from
Thanks in anticipation of your replies
Peadee.
PS... The hot water works fine.

 

[namsag]

Sounds like your pump has seized. Take the big screw out off the middle, you will get a little bit of water.
There is another little slot under this which you should be able to rotate with a screw driver if its seized then then you may need a new pump if you cant free it.
When you start CH you should see this spinning if it doesnt then pump is shot.
Pretty certain its Grundfoss 15/60 on these so you can just buy one of those and change the head leaving pump body in place

 

[Peadee]

Cheers Namsag.
Just had a look. I took out the large flat screw head and some water came out and continued to drip. Behind the screw head is the end of a shaft with a square keyway in the end. This turns freely with a screwdriver, does that mean the pump is gone and if so what is the most likely cause and can it be prevented in future? The boiler is only 2 yrs old.
Is this a job that I can do safely myself. I am a competant and careful DIYer.

 

[namsag]

With the first srew still off the pump start Ch demand and see if the shaft spins if it does it probably is not the pump

 

[Peadee]

The shaft does not spin, it just continues to drip.

 

[namsag]

Pump more than likely gone then . Take cover off side of pump and check for 240v with CH being demanded if there is 240 then pump has gone if no voltage the problem prob lies with the board.
IF its pump, pretty certain as said before they are grundfoss 15/60 although it will say bosch on it. You can just change the head, it is held in place with 4 allen key bolts. Takes ten minutes cost about 60 quid make sure you have it on speed 3.
Where as if you go for actual pump with specific body it will be well over a ton

 

[Peadee]

I've taken the side off and there are 2 red wires going into the pump and a Live, Earth and Neutral.
I cannot get my probe into contact with the Live and Neutral as it is. Can I remove the wires from the connection and test them that way just to make sure they are delivering voltage to the pump. Do I have to check for 240v or just volts, is there any chance of it being the wrong voltage?
Also do the wires just pull out, it looks like they do.

 

[namsag]

Yep power off first, disconnect live and neutral clips in pump just move back way. connect probes make sure not touching anything else. You should be getting 240 not just voltage

 

[Peadee]

OK, done that. My tester has 3 lights on it. 110v, 220/240v and 415v. The 110 and 240 ones lit up. I guess this means I have 240.
It gives the reading wether I have the heating switched on or not.

 

[sheffbodger]

I replaced the air vent cartridge on mine and last year and found it pretty straightforward. Just pulls out after you pull back a wire loop retainer. The part was around a tenner I think? I was told it's not an uncommon fault. I also bought some silicon grease for the O ring on it.
My symptoms were fairly obvious though; water all over the floor and a big stain running from the air vent cartridge!
The whole thing had been making some unpleasant banging noises just prior to this though...