Shower mixers need one way valves

[Temp]

Just a heads up...

 

Recently finished a second bathroom in our house and turned on the isolation valves for the shower. At first it appeared to work well but after a few mins the water ran cold. Its done that several times and it's not an issue with the boiler and tank running out of capacity.

 

I need to confirm this as the cause but I have a horrible feeling our plumber didn't install any one way valves. So at an unused shower it looks like water is flowing from the cold feed through the shower mixer and back to down the hot pipe, then to the shower in use. 

 

If that turns out to be the problem it's going to be "interesting" getting access to the pipes to install four one way valves as both rooms have stone tiles. 

 

I also think all four pipes are 22mm copper and run super close together in a stud wall so getting 22mm compression fittings in might prove a nightmare. 

 

Oh joy of joys.

 

 

[Thorfun]

Didn’t even know one-way valves were needed! Something else to add to my list to research. 
thanks for the heads-up and sorry to hear about your predicament. 

[Temp]

I've just discovered one of my shower mixers is supplied with non-return valves built in so perhaps I'm barking up wrong tree. I'm going to have to do some more fault finding. 

[Nickfromwales]

1 hour ago, Thorfun said:

Didn’t even know one-way valves were needed! Something else to add to my list to research. 
thanks for the heads-up and sorry to hear about your predicament. 

You do not need this with a "balanced DHW and CWS" system. Stand down Red Alert  

[Nickfromwales]

3 hours ago, Temp said:

Oh joy of joys.

Lets look at this pragmatically, first! .

 

Please remind me if you have balanced hot and cold supplies to each mixer outlet?

[Temp]

Think I'm hot on the trail of the problem. 

 

Found installation instructions for both mixers and they BOTH have non-return valves built in. So mighty relief as unlikely I will have to bash holes in walls after all.

 

On 15/04/2023 at 23:23, Nickfromwales said:

Lets look at this pragmatically, first! .

 

Please remind me if you have balanced hot and cold supplies to each mixer outlet?

 

The flows are balanced, all mains pressure and near identical pipe runs. However the hot goes through a heat exchanger on a thermal store. Water from the store is circulated through through the other side of the heat exchanger by a pump triggered by a flow sensor on the cold pipe. Eg open a hot tap and the cold flow starts the heat exchanger pump. 

 

Annoyingly the issue seems to have gone very intermittent. I was able to trigger the fault once and check the flow sensor was calling for heat (it was) but it started working again before I could check if the heat exchanger pump was running.

 

I'm leaning towards the pump or the supply to it being the cause but need it to fail more repeatedly to fault find it.

 

 

 

 

 

[markocosic]

8 hours ago, Temp said:

Found installation instructions for both mixers and they BOTH have non-return valves built in.

 

Which could also be filled with rocks, blebs of foam, and anything else that fit left in at the build / renovation / when the water board last dug up a pipe.

 

 

I've seen a 50 mm pebble from there incoming mains wedge a 100 mm fill valve open on a tank for a big block of flats once. Created quite the swimming pool did that...

[Temp]

We have burst watermains about once a year in our area. Think they are asbestos cement and it cracks when the clay moves.

Edited April 17, 2023 by Temp

[Mike]

11 hours ago, markocosic said:

Which could also be filled with rocks, blebs of foam, and anything else that fit left in at the build / renovation / when the water board last dug up a pipe

Yes, it's not often done domestically, but for the sake of a few pounds it's worthwhile adding a Y-strainer on the incoming water. Ideally add others before each pump and mixer.

[Temp]

I've found and fixed the problem. Not at all what I thought above and its been wrong for 15+ years !

 

It was the plumbing equivalent to connecting the neutral wire to the wrong RCD/RCBO. eg the live for a circuit connected to one RCD and the neutral connected to another.

 

We have a thermal store with two DHW outputs. One output has a secondary loop on it feeding remote outlets like the kitchen tap. The plumber had connected the kitchen tap supply to the wrong output on the store. This meant the secondary loop was drawing hot water from one outlet on the store and returning it to the other. On many systems that might not be a problem but there are heat exchanger, pumps and flow sensors involved.   

 

Anyway I've just spent the day cutting and soldering 28mm copper pipe to swap the kitchen supply to the correct circuit on the store. My better half is upstairs testing out one of the showers as I write. Haven't heard any screams yet.

 

The secondary loop pump is also a lot quieter  as it no longer has to push water the wrong way through a mixer. Surprised it hadn't gone on strike years ago. 

 

Edited April 27, 2023 by Temp