Cistern makes a bump end of flush

[Mrxman]

Hi There

I've had a new back to wall toilet installed with a new cistern. I switched mains water off for a few days while away and since I've come back and switched water back on the cistern makes a little bump at the end of the flush. It seems like it comes from inside the flush valve. Any idea why?

Thanks

 

[Wayners]

Water hammer?
You can fit a water hammer arrestor

You can also try backing the stop tap back a bit

 

[Mrxman]

Water hammer?
You can fit a water hammer arrestor

You can also try backing the stop tap back a bit

I tried backing the stop tap back which didn't make any difference. Will have a look at a water hammer arrestor.

Weird though that it was all fine to begin with.

Thanks

 

[dilalio]

Also ensure the correct restrictor is in the inlet to the fill valve.

If mains fed, should be high pressure one.

 

[Mrxman]

Also ensure the correct restrictor is in the inlet to the fill valve.

If mains fed, should be high pressure one.

Isn't the restrictor that comes with the cistern adequate?

 

[dilalio]

Isn't the restrictor that comes with the cistern adequate?

Usually they have a high and low pressure one.

And you fit the appropriate one.

Depends on the valve.

When I do a combi conversion it's important to check the cisterns as they will usually have low pressure orifices fitted and now on mains, they'd rob all the flow when flushed... Not good if someone is in the shower!

 

[Mrxman]

Usually they have a high and low pressure one.

And you fit the appropriate one.

Depends on the valve.

When I do a combi conversion it's important to check the cisterns as they will usually have low pressure orifices fitted and now on mains, they'd rob all the flow when flushed... Not good if someone is in the shower!

Great, will have a look. So is this bump I notice in flush valve a common occurance? I am asking because the manufacturer had never heard of it before. Maybe a predictable response from a manufacturer.

 

[dilalio]

Great, will have a look. So is this bump I notice in flush valve a common occurance? I am asking because the manufacturer had never heard of it before. Maybe a predictable response from a manufacturer.

Any valve that shuts off quickly can cause a thud or bump.

May not be from that valve but elsewhere on system.

Would suggest first taking it apart and cleaning it out. Maybe diaphragm dried out or has crud in it.

That first and check for restrictor.
Then look at a shock arrestor somewhere on the cold feed.

 

[Mrxman]

Any valve that shuts off quickly can cause a thud or bump.

May not be from that valve but elsewhere on system.

Would suggest first taking it apart and cleaning it out. Maybe diaphragm dried out or has crud in it.

That first and check for restrictor.
Then look at a shock arrestor somewhere on the cold feed.

Thank you. Much appreciated

 

[dilalio]

Thank you. Much appreciated

Np.
Good luck.

 

[brig001]

Is it on both flushes - long and short?
We have one that bumps only on the short flush, but I never got to the bottom of it - concealed cistern and I can’t be bothered while it’s still working
Brian

 

[Mrxman]

Is it on both flushes - long and short?
We have one that bumps only on the short flush, but I never got to the bottom of it - concealed cistern and I can’t be bothered while it’s still working
Brian

Both flushes. It's a bit less now though. As far as I can tell it's the flush pipe, there's a bit in there that hits the bottom when flushing but haven't actually taken it apart yet and cleaned. Had a thought that maybe it's because it's a cheap cistern.

 

[dilalio]

Both flushes. It's a bit less now though. As far as I can tell it's the flush pipe, there's a bit in there that hits the bottom when flushing but haven't actually taken it apart yet and cleaned. Had a thought that maybe it's because it's a cheap cistern.

When you say flush pipe, do you mean it's a low level cistern with pipe connecting it to pan?

Might need cutting down a bit as sometimes the flush pipe can protrude too far up into the cistern and flush valve may be hitting it!

 

[Mrxman]

When you say flush pipe, do you mean it's a low level cistern with pipe connecting it to pan?

Might need cutting down a bit as sometimes the flush pipe can protrude too far up into the cistern and flush valve may be hitting it!

Apologies, got terminology mixed up. It's the flush valve where the bump comes from. It seems to have decreased slightly but I may still clean it out as you suggested.

Btw, one other question. The back to wall toilet is stable and firm but when I put my hand on the silicone seal behind the toilet and wiggle a bit there a tiny amount of flex. Not enough to break the seal though, just a tiny bit. Is that normal?
The guy who helped me put some shims underneath toilet but wouldn't have thought that would be a problem.

 

[dilalio]

Is that normal?

It's fine.