Electric shower replacement also going hot and cold

[Phil]

I replaced an old heatre sadia electric shower with the same KW (8.5) mira jump.

The new shower has the same fault as the old one going hot and cold. When I tested it all seemed well with good water pressure.

 

[rocketmanbkk]

Water pressure?

 

[Phil]

Water pressure is good in the house.

 

[rocketmanbkk]

Very strange it's the same issue. I'm no expert.

 

[JCplumb]

The only obvious thing I can think of that would cause hot/cold running (providing the shower is not faulty) is the thermal cut out.
Is it very hot then cold? Maybe try turning the temp down a bit or run it on the econ setting to check if it's the thermal cut out kicking in.
You'd be very unlucky to have a new shower that is faulty, especially one showing the same problem as the one you took out, but it's possible.

 

[Phil]

I'm going tomorrow to have a look, dragged away from my warm fireside to have a look at something I can only assume is a dodgy pull cord switch ....its an old round one.
I

 

[Shower Engineer]

Phil, I doubt it will be the pull cord. Take a look at JCplumb post for the most obvious answer. Cycling on the TCO is a big problem, just turn the temperature down a bit and then see if the temp is steady. Only other thing to check is did you replace the hose and hand spray?

 

[Best]

My first thought was pull cord switch, - bad contact inside it on one of the 2 switch parts or neutral or live wire connections inside it. Replace it with a 50 amp pull cord. Seems the original shower ain't faulty.
I find the pull cords to be burning out all the time. Badly made switches.

 

[Best]

As Shower Engineer says, - hope you replaced hose and hand set as if they are blocked then reduced flow will mean hotter water

 

[Best]

In thinking about this, - surely if water pressure is good, then the shower will not cut out often on the thermal cut out unless the shower temperature knob is turned to very hot?

 

[Shower Engineer]

Best, No it wont but what happens is that someone either sets the temperature too hot or the pressure isn't great and somebody turns a tap on. Turning the tap on causes the pressure switch to drop out and the shower goes cold. The tap is then switched off and the pressure restored but in the meantime the person who is now shivering in the shower has turned the temperature up so the shower is now too hot. Most people shower between 38 and 42 degrees and most TCO's cut in at 47 degrees so there is not much margin for having a shower set too hot.
Hope that makes sense,
Dave

In thinking about this, - surely if water pressure is good, then the shower will not cut out often on the thermal cut out unless the shower temperature knob is turned to very hot?

 

[Phil]

All new hose and showerhead.
I'm clutching at straws with the pull cord...I'm going to check water pressures and make sure everything is fully open.
I replace loads of showers and never have a problem, other shower was 10 year old.

 

[Best]

Best, No it wont but what happens is that someone either sets the temperature too hot or the pressure isn't great and somebody turns a tap on. Turning the tap on causes the pressure switch to drop out and the shower goes cold. The tap is then switched off and the pressure restored but in the meantime the person who is now shivering in the shower has turned the temperature up so the shower is now too hot. Most people shower between 38 and 42 degrees and most TCO's cut in at 47 degrees so there is not much margin for having a shower set too hot.
Hope that makes sense,
Dave

I have never seen that happening, - except if testing a new electric shower at a full heat (knob turned to little flow). Also never seen that happening with a tap somewhere turned on, but that just probably doesn't happen any times I have tested showers.
Although by the sounds of the OP the flow was good and unlikely that everytime the shower is tested there is a tap getting opened.
Thanks for that, - it does explain it very well.

 

[Best]

All new hose and showerhead.
I'm clutching at straws with the pull cord...I'm going to check water pressures and make sure everything is fully open.
I replace loads of showers and never have a problem, other shower was 10 year old.

Looks like you will have to run the shower at full cold to see if flow remains very good and then try it at one element half heat setting first.
If it was the pull cord faulty, I guess the entire shower would turn on and off if bad connections inside pull cord. Although I would never rule out pull cord and some showers have phased shut downs.

 

[spanner]

Yes. Try post in #5, and I must say that I have hope this shower has come out of the "new box" and to the installation. And not one that's been laying down for a while!
As this is what happens when you suddenly get a mad crazy shower sale.
They have to go..
But deffo not the pull cord! No way!
Either has to be a pinhole in flow sensor diaphragm. Flow sensor probs!
As you know it's mains water feed. Would applying prv to regulate the constant flow..
Nevertheless. It should not be going in and out hot cold.

 

[thompsonbrown]

The flow rate of water through the unit could be too low, causing the thermal cut-out to activate. Check there are no blockages in filter.
There could be a possible sudden drop in water pressure, falling below the minimum required. This could be because water is being drawn off elsewhere.
Only other thing might be a break in the cable causing it to make and break when current is flowing.

 

[Phil]

Went to see this tonight, it may be there is nothing wrong with it.
With the temperature dial set to about 1'o clock it runs fine, when you turn it right up to very hot at around 3'o clock it becomes affected by flushing the toilet and it goes cold for a few seconds.

But is unaffected by toilet flushing at 1'o clock position.

Water pressure at the shower is 5 bar with 0.5bar running pressure.

I replaced the switch to no effect.

 

[rocketmanbkk]

Yeah, that happens, my neighbour called me in few weeks ago as elec shower was poor flow, on full cold very good, full hot trickle, warm ok.

 

[spanner]

Check inlet filters. Flow rate must be mains minimum fed required.