Dudley syphon. Flushes first time but won't flush again for a few minutes although cistern is full

[Joef]

Dudley japtic syphon. The first flush works fine, the cistern fills up fully straight afterwards, but when you try to flush again it doesn't flush. You can try a few more times and it still won't flush. Leave it 3-4 minutes and it flushes fine again.
Should I just replace the syphon or washer part or is there something else that is so obvious that I could do to make it flush again once the cistern is full after the first flush?

 

[jtsplumbing]

What is the water level like should be a mark inside the cistern what syphon have you fitted (Turbo 88) or another sort.

 

[Joef]

The syphone in there is really old, I didn't fit it, it's not the turbo 88 I know it as a dudley japtic 9' syphon. When I flush it the second time the water in the cistern has risen back to being full it just takes a few minutes before it will flush again weirdly. It is a bit odd but that is really what happens.

 

[Daniel Hall]

Just fit a new syphon

 

[Ric2013]

I reckon the flap valve in the siphon has become stiff for some reason. You'll probably have to take the siphon out to be able to check it anyway.

 

[Joef]

Cheers all. I was checking to see if I missing a simple trick and trying to be overly economical, hard times and all that. I'll take it out and have a look to see if the flap valve needs replacing or the whole thing.
The dudley turbo 88 is just the more modern version that easier for maintenance work right?

 

[jtsplumbing]

Yes but twice the price

 

[sammathias]

Sounds like syphon is on its way out... Low level cistern and wc pan? Pipe between cistern and toilet? If so probably partially blocked with syphon washer.