wc cistern - sudden loss of water flow

[newbuyer17]

I have a w/c with on of these cisterns.
http://www.siamp.com/index.php?option=com_hotproperty&task=view&id=36&Itemid=42

Its about 5 years old and has always worked great. But today, it still works, but after flushing, the tank is taking nearly an hour to fill up. It is pretty badly enclosed so I can't really get in to see why, but the flow coming out is very limited. Works OK though, and float valve moves freely. Just takes ages between flushes.

I'll take it all apart in due course, but would like to have a good idea of the problem to get spares in advance to fix in one go. Is this a common issue? Am I correct in assuming I just need to replace the float valve unit? If so will a generic one do, or will it be specific to Siamp.

Anything else I should be looking for?
1. We live in a hard water area, though I doubt it could block this suddenly?
2. Its covered in black mould, but as I said it moves freely.
3. Shower, bath taps on same mains feed all have good pressure, so dont think my overall pressure has dropped.
4. No leaks that I can see.
5. I seem to remember when fitted it had a mesh washer over the inlet. Could it be this has become blocked with something, and I just need to unscrew and replace?
6. Or am I looking at a new float valve?

Anything I've overlooked, or is my reasoning sound.
Thanks in advance, any advice would be greatly appreciated. As I said this is a bugg 3r to get to, so I want to do the lot as one job.

Thanks
Edit: If it helps, this is the float valve I'm referring to.
http://www.toiletspares.co.uk/siamp_spares_19.html
It will be one of the bottom entry ones - not sure which yet though.

 

[supergas]

these valves usually have a filter in which could be blocked,
any valve will work but it must fit in the box without touching sides as this could stop it working.
im guessing the cistern is in a vanity unit with very little access, if so then the cistern will have to be removed in order to change the valve (quite easy).

good luck. !

 

[supergas]

also check on inlet for an isolation valve and check it.

 

[TicklyT]

It sounds like only the pilot valve of the fill valve is opening. There may be a bit of crud stuck in the pilot valve, which is little more than a pinhole, or in the diaphragm chamber behind it so it doesn't release the water pressure that holds the main valve closed.

 

[newbuyer17]

OK, thanks people. That gives me a few things to look at.

Just need to decide whether to mail order a Siamp one in advance that I might not need, or to rely on running off and trying to get a generic one that fits if it turns out not to be just a blockage.

 

[supergas]

we normally change them for new anyway to save messing, any slight fault we just change them (comes out of the boss`s pocket )