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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> When OFF doesn't mean OFF..... https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1592028975 Message started by londonman on Jun 13^th, 2020, 7:16am

Title: When OFF doesn't mean OFF.....
Post by londonman on Jun 13^th, 2020, 7:16am

...or why a Hans Grohe iBox is such a silly design.

So, you learn something new every day. Fitting a new ensuite as part of the whole house refurb.

Finally, all systems go. Time for a shower.

Scenario...our house has two separate pumps for cold and hot water. The cold pump (historic) is in the cellar. The hot water pump is new and installed upstairs next to the HW cylinder. I can hear it when it kicks in and once the hot water is pressurised, it stops.

So into t'shower, turn it on (separate control) and wallow. Have shower. Turn it off. Only ....only ..

only the H/W pump does not stop. Thinks...this should not be happening. I've tested it before it was all tiled up. There are no leaks. It should not be doing this. Switch off the H/W feed to the ensuite at the manifold. Pump stops. Sh*t. I must have a leak somewhere. I have an inspection hatch. No leak. WTF ?

Engage brain. Where can it be pumping to? 'cos it is - otherwise it would pressurise up and stop.

Back up the cold water feed ? Surely not ? Switch off cold feed at the manifold and the H/W pump stops.

And that is when I realised that OFF on this Hans Grohe cock-a-mamie iBox is only off as far as the shower head is concerned. Both cold and hot feeds remain 'live' relative to each other and so if there is an imbalance in pressure then one pumps into the other. The 'fix' is to turn off the temp control on the iBox but what a faff...annoying, to be sure....but even then there is still a slight bleed of water through back into the cold water pipes and so the H/W pump kicks in...on and off.

I think a checkvalve in the cold feed will sort it.

Title: Re: When OFF doesn't mean OFF.....
Post by thescruff on Jun 13^th, 2020, 9:38pm

System Design fault, usually a secondary circuit.

If either or both pumps are not pressurizing you have an open circuit, so the first task is to find where the water is going other than around and around.

Both pumps should be protected by double check valves.

Ideal world an as fitting drawing, please.

Title: Re: When OFF doesn't mean OFF.....
Post by londonman on Jun 13^th, 2020, 9:54pm

I can assure you that the only design fault is the Hans Grohe iBox. The rest of the house has a multitude of mixer taps, thermostatic shower controls etc. All work perfectly well. When you turn them off, they do turn off. Cold and hot both pressurise up and the pumps stop.

The i Box has no such luxury. The only on/off is on the output of the mixer. So hot and cold circuits commune together quite happily because they are nit turned off. I can understand that the iBox will work perfectly well if it's installed in a house with, say, a twin Stuart Turner pump because both hot and cold will be of equal pressure...more or less.

But if there is an imbalance between the two of sufficient magnitude then whichever circuit has the higher pressure will force back into the other.

It's simply a duff design and I'm surprised that Hans Grohe have designed it this way.

Title: Re: When OFF doesn't mean OFF.....
Post by thescruff on Jun 14^th, 2020, 10:58am

If you say so lol.

So one or more pumps is not turning off?

Where is the water going?

Title: Re: When OFF doesn't mean OFF.....
Post by londonman on Jun 14^th, 2020, 10:07pm

Well, I'm not an expert on pumps. You're right in that if one pump is running then the water must be going somewhere. My conclusion is that it's flowing back through the cold water pump into the clean tanks. Cos there isn't any leak anywhere.

Because you mentioned that the pump should be protected by a double-check valve (it isn't...none of them are..we have five....all here before I came) then it must be feasible for water to be forced back through a pump.

Title: Re: When OFF doesn't mean OFF.....
Post by thescruff on Jun 15^th, 2020, 10:39am

High-risk Legionella.

Title: Re: When OFF doesn't mean OFF.....
Post by londonman on Jun 15^th, 2020, 6:12pm

Good point. The double-check valve arrives tomorrow which should sort it out. I say 'should'.

I have four separate plumbed areas in the house - each fed from a manifold via a gatevalve. [gallery]londonman/1592240657.jpg[/gallery]

The one on the extreme right is feeding the ensuite in question. There are three 'outlets'...the WC, handbasin and the Hans Grohe shower control.

So just to recap...all works in the ensuite until I come to turn the shower off. The shower stops flowing but the hot water pump still keeps running. If I turn off the cold gate valve (extreme right in picture) then the h/w pump stops. If I turn off the Hans Grohe temperature to its coldest then that (sometimes) will also have the same result.

So this evening I thought...if my theory is correct then if I adjust the Hans Grohe temperature control to, say, mid-point, turn off that gate valve then if I flush the WC then the H/W pump should kick in ...but it doesn't !

I really have no idea now what's going on ! AllI know is that I have no leaks !

Title: Re: When OFF doesn't mean OFF.....
Post by thescruff on Jun 16^th, 2020, 1:21pm

Which is why I asked for more information.

what is the make and model of the pumps.

could still do with an as fitted drawing.

After you turn the shower off, what happens if you turn the power off to the pump, count to 10 and turn it back on again, I get the impression the pump wasn't running before you had a shower so why should it run after you have had a shower.

Have you installed the iBox the right way round, are you using the top or bottom outlets or both,

which model iBox is it and what controller.

ps, don't fit the check valve yet,
where were you thinking of putting it.

You do realize the controller can have a backflow.

The red valve is the cold feed to the cylinder, is anything else connected to it.

My problem with the install.
Hot pump is fed from the cylinder, and the cylinder is fed from the pipe with the red valve, therefore the pump is sucking out of the cylinder and the cold feed.

It cannot suck and blow the same pipe.

How can you pressurise an open vented system.

Title: Re: When OFF doesn't mean OFF.....
Post by londonman on Jun 16^th, 2020, 4:44pm

You're making assumptions that are incorrect. For example, the cylinder is fed from a cold tank in the loft. Historic reasons.

Anyway problem solved. Hans Grohe are supposed to have fitted backflow preventers inside the shower controller. They are missing and so they are sending me a set.

Title: Re: When OFF doesn't mean OFF.....
Post by thescruff on Jun 16^th, 2020, 11:52pm

My assumptions are perfectly correct, yes the cylinder is fed from the tank in the loft via the pipe with the red valve, guess as there's not another valve it could be.

anyway let's hope you have it sorted