Leaking bottom inlet on toilet cistern.

[Bogart]

Just fitted a new WC and all okay except I cannot get the bottom water inlet to seal. It is a Fluid master setup. It drips from between the cistern base and the plastic nut not between the nut and the thread. It came with a flat washer, have even tried 2 washers, came with a spare in case cistern had side entry too. Now some Fluidmasters come with conical washer, like those used to seal the cistern to the pan, not sure how it is decided whether flat or conical, not what to use to overcome this problem.

 

[Rob Foster]

I always thro away the foam donut and get the rubber one
more reliable and re usable
centralheatking

 

[ShaunCorbs]

Con washer always

And is the cistern flat around the inlet hole eg no bumps / lumps in the casting

 

[steadyon]

Conical washer inside cistern with narrow end facing down. This makes the water tight seal between valve and cistern, and also centralises the threaded stem of the valve in the hole in the cistern. On outside of cistern, no need for a washer, just the white plastic nut.
Make sure you have a fibre washer in the connector which secures the inlet pipe to the bottom of the inlet valve, unless you are using a flexible hose to attach, in which case there should already be a rubber washer inside the flexi connector.

 

[Ben-gee]

As shaun says, check base for lumps/bumps in the glaze - I would add to that check for hairline crack.
Conical is best but to be honest you should be able to seal against the 0.03bar head with a flat washer.
For fail safe run a bead of stixall/ct1 under the flat washer first and then tighten as usual.

 

[Bogart]

I always thro away the foam donut and get the rubber one
more reliable and re usable
centralheatking

Hi It is the water inlet not the cistern to pan joint.

 

[Bogart]

Con washer always

And is the cistern flat around the inlet hole eg no bumps / lumps in the casting

Looks to be fine even so I ground out a couple of minor bits and feels smooth enough.

 

[Bogart]

Can you buy the conical washers separately? Off to TS to get a tube of Stixall.

 

[ShaunCorbs]

If it’s smooth how tight are you doing the nut up ?

 

[Bogart]

If it’s smooth how tight are you doing the nut up ?

Started at finger tight, then a bit more ,and then a bit more .