Has anyone installed a gurgling flush valve before?

[JoVil]

I just installed a Fluidmaster dual flush valve (screwfix code 51173) in a concealed cistern and when flushing it makes the most horrible suction/gurgling noise as the water exits the cistern tank down the flush pipe until the flush is complete.
I've adjusted the volume of water flushing and adjusted the attached (internal) overflow to see if that's causing it, but nothing seems to work.
Blocking the overflow with my finger silence the loud noise, but you can still hear there's some sort of vacuum forming or siphoning as it flushes.
I can't for the life of me work out what's causing it. I have never had this with any flush valve before on either concealed or close coupled.
Does anyone know what it could be. If not, which flush valves do you guys recommend?

 

[oz-plumber]

What height above the pan is the cistern?

 

[JoVil]

Good question. It's about 13 inches or 330mm. What's your thoughts?

 

[rpm]

Something from the old valve stuck in the flush pipe?

 

[plumbdoctor]

Not one of them old toilets that has the breather hole ? Does it back up in the pan before finally going away ?

 

[PETE 123]

Supply the customer with ear plugs

 

[WaterTight]

is it the flush valve emptying the whole cistern and does the gurgling happen at the very end?

 

[JoVil]

It's a new back to wall installation and nothing in the flush pipe. The gurgling start almost as soon as the flush starts and stops when it's empty. I flushed without the pan in place ie running it into a bucket and the noise persists. I am curious about the Aussie's question about the height of the cistern above the pan though. Can that make a difference? If not I'll just get a replacement with a different design. Which brands do you guys rely on for minimal long term maintenance? (Hope that's a legit question on the forum). Thanks for replying!

 

[JCSPLUMBING]

Geberit if you can afford one. I can't so I go with whatever's cheapest in screwfix. Usually about £10-£15 or so

 

[tolly]

I use fluidmaster flush valves a lot and have no problems with it, something else is probably causing it...I don't know what though,

maybe try twisting out the flush valve and then poor a bucket of water down the cistern, if it still gurgles the problem is not the fluidmaster.

 

[Unregistered]

Tolly, I've twisted and pulled it out quickly when full to let it run empty a few times and it still makes the noise. That's what's so mysterious. The noise seem to come from where the overflow meets the bottom of the flush valve. I've also only used fluidmaster unless flush valves comes supplied with wc. Never had this before.

 

[oz-plumber]

Good question. It's about 13 inches or 330mm. What's your thoughts?

I bet this isn't the only forum you have posted those measurements on!!

Back to Plumbing... that height shouldn't have any effect on the cistern flush. Sometimes concealed cisterns are placed in the ceiling and require baffles in the flush pipe to slow the water flow into the pan.

Is it an original flush valve or an after market product?
If it's an after market product, you may want to try on original product.
Probably be 3 times the price though.