Constant Dribbling Rain Head - Syphon effect? Diagram...

[Ben B]

When I moved to my house the ensuite shower was out of use due to a
stuck valve on one of the inlets
Anyway it was out of use, so I actually never tested it with it's original hose set up, and completely rebuilt the shower room, with a new cubicle and rain head before finally fixing the mixer and then finding it dribbled constantly.

I called Grohe support who (In the last month of warantee!) sent out an engineer who eventually had to replace the whole unit to get it to not run constantly.

That was 6 months ago. Recently it started to drip again, getting so bad recently that we've had to turn the water off to it, as it dribbles so much we can't sleep in the room next door!

I'm a little baffled, it can't be the cartridge/any washer as it's 6 months old.

I'm thinking (and this is where I need advice) that it's to do with my plumbing between the mixer and the rain-head.

My theory, that I'll test tomorrow is that if I disconnect outlet from the mixer it won't dribble. If that is the case then somehow water is getting pulled through the system due to the unusual shape that the pipe takes.

Here's my theory, can anyone advise if it's nonsense!:

Here's a diagram of the pipe to the rain-head (in red):

Untitled

• Ben B
• 9 Jan 2009
• 1

The sloping roof-space seemed impossible to run a pipe through, plus the ceiling above, so in the end I shaped a 15mm pipe with a couple of kinks and pushed it up into the loft space where it meets a vertical pipe, that runs under the shower tray and joins.

My crazy theory is that the last few feet before the rainhead, at 45 degrees, has water falling out of it when the shower is off, and somehow, even with the mixer turned off, the syphoning effect is enough to pull more water through.

Is this possible?

Or is there a much simpler theory? Why is it dribbling so much? How can I stop it! (Even with the head off it dribbles of of the pipe)

 

[mogget]

It can't be syphoning, because the outlet is higher than the inlet - it would be a perpetual motion machine!

This leaves two possibilities that I can think of:

- The valve is letting by

- The dripping is simply from water left standing in the pipe, and the drip would stop if it were left alone for long enough.


The fact that it stopped for a while after it was serviced does suggest the valve is letting by. My suspicion is that scale or crud is getting into the valve and causing it not to seat properly. Some shower valves have little filters on the inlets to lessen the chance of this happening.

 

[Ben B]

Thanks for your reply;

The water continues forever, so it's not just in the pipe. I dis-proved my silly theory anyway today- I disconnected the outlet from the mixer and it continues to drip from the mixer, so it's definitely just the furring up of the internals from our hard water.

I've removed the unit completely, removed all the circlips etc to get all the knobs etc off the front, but for the life of me can't get the main unit completely apart. (it's a Grohe Avensis Classic if anyone's familiar!)

Seeing as I'm not a professional I figured I'm likely to do damage if I do get inside anyway, so here's my idea:

If I leave the unit to soak in white vinegar for a day it will clean the insides out!

But will the vinegar damage the thermostatic valve/cartridge??

 

[mogget]

here's my idea:

If I leave the unit to soak in white vinegar for a day it will clean the insides out!

But will the vinegar damage the thermostatic valve/cartridge??

I wouldn't have thought that would damage the valve, but I must warn you that I don't have any experience of vinegar and shower valves! Perhaps someone else could confirm?

If the problem is limescale then the vinegar will dissolve it, but it may not work on other types of crud.

If the valves inside are ceramic they may be damaged beyond repair.

Because this is a recurring problem, once it's fixed it would be wise to take precautions to prevent it happening again.

 

[Ben B]

What can be done though, except install a water softener?

I know what you're saying though it's just gonna happen once a year otherwise!

 

[mogget]

Filters on the inlet pipes should do the trick - the scale / crud won't be forming inside the valve but travelling in from somewhere upstream. How is your hot water heated?

 

[Ben B]

The house has very good pressure, from a presurised Heatrae Sadia boiler or however it's spelt.

I didn't realise you could filter the water on the inlets

 

[mogget]

Many shower valves come with filters, these look like tap washers but there's a gauze in the middle instead of a hole. I think a plumbers' merchant will probably stock them, or maybe one of the larger DIY sheds.

 

[Ben B]

Well, I put the whole shower mixer unit it a vinegar bath for about a day, took the rear cap off, but couldn't undo the big nut that holds the front on, so left that together.
Reinstalled it, and it dribbles just as much. So I guess it's not limescale at fault? So logically it must be something else caught in the system, like a piece of ptfe worked it's way round the system or something.

Not I'm gonna have another go at removing the internals, see if anything obvious is in there.

I'm really really baffled though. The same thing happened 6-8 months ago, the internal parts were replaced and it still happened, so they ended up replacing the whole unit for me. I don't know what could be causing it!