Power Shower: air lock forming in shower head?

[Potemkin]

I have a power-shower that works very well. Except, when I switch on the water, nothing comes out of the shower and the pump doesn't make a sound. I then have to lift the shower head off its hook and shakeit around for a moment; whereupon suddenly the pump kicks in and the shower works like a dream.

If I turn the shower off, then immediately back on again, it works fine. If, however, I leave it off for 30 seconds or more, I then have to go through this routine once more.

I presume that water is draining out of the shower head, and an air lock is forming somewhere between the wall outlet and the head: wiggling the shower head moves the bubbles and water can pass? Is this correct? If so, what can I do to prevent it?

There is a non-return valve inside the wall-outlet, which I presume is working fine, but maybe this is another possible cause?

Many thanks....
Potemkin

 

[Softus]

It's possible that the shower and pump haven't been installed correctly.
It's also possible that the pump is the wrong type for your application.

More information is needed....

How long have you had the shower/pump (or how long have you lived there)?

Has it always [to your knowledge] had this problem?

What's the make and model of your pump?

 

[Potemkin]

The shower has only just been installed. The pump is a Stuart Turner 3 bar twin pump.
Thanks
Potemkin

 

[Gasguru]

Is this refering to the same lash up in your other postings?

Previous postings refered to a different 3 Bar pump but the plumbing was a mess and would never work properly.

Install the pump next to the cylinder.

Install a seperate cold feed (min 22mm) from the cylinder to the pump.

Come off the cylinder with a proper flange fitting.

I would get rid of the Speedfit since it can trap air with its restrictive fittings.

Are you complying with the minimum shower head to cold water tank heights in the manual?

 

[Potemkin]

Yes,
same setup.
The building firm sent round some new plumbers, who spent a day "fixing" the plumbing as follows:
Fitting flange into the bottom of the HWC
Replacing air valve for "correct" kind
Fixing some of the speedfit joints that were poorly done

However, speedfit pipe still used for entire run up to the pump, and pump is still a long way from HWC. To move this pump now would mean taking out the shower glass, tiling, & stud walling, as the builders basically entombed the thing behind the shower cubicle. The firm assured me that this would now work, and true enough it does once you shake the shower head to get water moving... am I being optimistic that this could be a simple issue with the shower head rather than the same poor installation issue?

 

[Dan Robinson]

So what happens in 5 or 6 years when the pump needs a new flow switch or some such? Why is there a flange in the bottom of the cylinder?

Why did you take their assurance at face value without thoroughly testing it whilst they were there?

To me this sounds like a real hash job.

Instead of shaking the shower head, just try lowering it gently toward the foor. Does it come on then?

 

[Potemkin]

The benefit of hindsight...
Well, you're onto something. I tried the trick of lower the head gently, and it starts working when I drop it half way to the shower tray. Every time. Interestingly, this is the exact height of the shower pump behind the tiling.

Weird thing: we did test the shower and it was working fine when the plumbers redid the pipework. However, at that point we had deliberately not fitted the shower glass, in case we needed to open up the wall to get to the pump, so I expect we tested the shower in hand rather than on the hook, to avoid spraying the room with water.

We then fitted the glass, and hey presto because the head is on the hook, it's not far enough below the water tank (or whatever) and so we experience this problem.

Perhaps we need to raise the cold water tank. I would say, roughly, that the bottom of the CWT is about 6" above the shower head level.

There is an access hatch in the wall through which a man can reach the pump, but only just... it's not ideal at all.

 

[Dan Robinson]

The force is strong with this one. Spidey senses were indeed tingling.

I would say, roughly, that the bottom of the CWT is about 6" above the shower head level.

There is your problem!

So half way down the shower would make a metre form the tank - the minimum head of the pump.

They should have installed a negative head pump.

 

[Potemkin]

Why oh why does it take a posting to DIYnot to get a sensible answer to these questions: the building firm are currently playing dumb, perhaps because this could be expensive to fix. Anyway, thank you for your most valuable help.

I've retrieved the instructions for the pump:
"For the pump to function correctly, it must be installed in a +ve head position, a gravity flow of approx 0.6 litres per minute is required from the highest outlet to operate the built-in flow switch. This is normally achieved with a static head of 100 mm from base of header tank to highest position of the shower terminal fitting.... the pump should have a min. inlet head of 1m."

Let me make sure I've got this right: the shower head is probably just on the 100mm minimum (or thereabouts), and the pump is just about 1m below the cold water cylinder. This is just about acceptable, but when you consider that the pump is 20m from the HWC, and having to pull rather than push water, the pump is struggling to feed the shower effectively. The answer is to resite the pump or to lift the cold water tank up a foot or so?

 

[Gasguru]

Complete bodge job

Bet you haven't got full bore isolating valves on the pump either - lets hope is doesn't go wrong.

Chuck out the speeedfit and use copper - this may reduce the friction sufficent for the pump to start up.

Consider raising the cold water tank.

Take a cold feed direct from the tank to the pump.

You sure the flange is fitted at the bottom of the cylinder - if so you won't get much hot water.

Make sure your hot water temperature from the cylinder is no more than 60 centigrade - with the pump you have and the location/pipework you risk killing the bearings.

Forget the warranty with the pump with this installation it will be invalid.