Theromstatic shower only turns on if using handset first

[rivergo1d]

Hi
We have a 2-way shower with a rain head and a shower handset.

If we turn on the rain head from scratch, no water flows through. We need to turn on the handset first, get water flowing through that, and then swithc to the rain head, and then water flows through it.

We believe this works because of the pressure head difference between the two. Recently we have started having to lower the shower handset for this trck to work - ie creating a greater pressure head - and so we are worried that eventually it will stop working completely.

Does anybody have any idea what might be causing this?

 

[Jordon]

Does it have a pump?

 

[HERTS P&D]

Negative head pump will be needed. As not enough flow for rain head to turn the pump on.

Andy

 

[rivergo1d]

Thanks guys, the pump was my thought too but I didn't want to prejudice people's opinions.

It does have a pump, I find if I turn the flow to cold rather than hot then this can sometimes kick start it too. So it all points to the higher head of the cold tank being "just enough" to kick start it.

The same pump system used to work. Changes are:-
1. New shower with new head, valve
2. Some 22mm speedfit piping in the shower area.
3. New valves fitted in the copper lines out of the loft tanks

I didn't think speedfit in the shower will have such an effect, but am wondering whether the reduction in bore with the new valves could also be pushing it over the edge. Don't know if they're full bore or not.

One thing that puzzles me is another shower at much the same level never has problems - that shower is one of the ones from a bath mixer, so perhaps less complicated valve system makes the difference? Not sure how that correlates with head ...

 

[Jordon]

Problem is that someone had fitted a modern fitting that prob has non return valves in it also so will need a higher min pressure to work,change the pump to a negative head all will be good again.

 

[picasso]

I would check the new valves in the loft are full bore before changing the pump, it might just be a restriction caused by the small bore tank valves thats causing your problem, neg head pumps aint cheap.

 

[rivergo1d]

Thanks everyone! First port of call will be the valves in the loft, if they're not a quick fix then I need to weigh up the inconvenience against the cost of converting my pump to negative head.

The survey for the house did say that the water tank wasn't adequately supported so raising and reinforcing that could be a further option...