Another Mira Elite St question

Did you try the calgon? Just noticed you were saying it was going from cold to too hot, is it from fully cold? I was reading it as going from too hot to cold. I`d a few too many the other night while posting for:).

If it was something like the pressure switch closing (which is to ensure the elements dont come on with no or too little water), then it would be going from fully cold to hot.

The pressure switch is after the heating tank as it goes to the shower head hose, so its between the tank and shower head.

This means a clogged head will reduce flow rate but increase pressure in the shower, so pressure switch stays on, and shower is just too hot right through the dial range.

A clogged/scaled element tank though, will reduce pressure on the outgoing side of the tank, so the water would have to be turned up that bit more to get the pressure switch to close, but at this flow rate, the shower may be too hot, so it switches from fully cold to too hot.

It might be none of the above, but if its from fully cold to too hot its going, its a good possibility. A simple test is to partially restrict the shower head holes while its running too cold, with a cloth etc, and this would close the pressure switch, and you would feel the water warming then with cloth still partially restricting the flow.

All of the above is only if its fully cold but changing to too hot on a dial temp increase.

Where did you put calgon as mattter of interest, direct into the shower tank? I`d say direct into shower tank itself would be worth while to see if it helps. An interesting one that.

Yea that might work alright, maybe break the tablet into small crumb size pieces. Best way of all would be to remove the tank from shower and fill it with water and calgon while its removed. Not sure what the tank is like to remove from that particular one.


If the problem is the pressure switch operating as you move dial slightly, what would be noticed is that you would probably be turning the dial in the temperature cooling direction to make the heat come on, and in the temperature increasing direction would make it go cold. The same thing would happen if its the overheat cutout operating due to limescale, but if its the pressure switch operating, once it goes cold, it will stay cold without the heat coming back on if you left the shower running for a couple of minutes. If it was the overheat cutout, the heat would come back on again itself. So it might be worth leaving it running a few minutes when it goes cold to see.

Not sure if the pressure switches themselves go faulty in them, which would be another possibility maybe. Easy enough to test if it is the pressure switch operating with a meter. Needs to be done with shower running though.

Sometimes something simple we would miss in these matters with showers, like everything else electrical as you know.

When elements are covered in scale, the water now does not remove heat from them as efficiently, so they overheat, and operate the cutout. Now the elements will cool, but again because of the scale, they wont cool near as quick as clean elements will, so while the heat on and off will cycle with the overheat stat going on and off, it will take a while.

So if your dial positions are as per top one at medium, and bottom one(temperature) up near its highest(red end of dial), then it is the overheat cutout operating when you have the elements all on. And de-scaling should fix that.

Thats good anyway, once you had said it worked on low heat(1 element off), it seemed the likely cause alright.

My own t90 is beginning to cycle. I will probably remove the tank from it and de-scale that way. Scale seems to be causing a lot of shower problems.

Maybe an easy way to introduce de-scaler into the shower heating tanks by the manufacturers would be a possibility.

Stoner wrote: »

I had industrial descaler, given to me by a friend, good stuff by all accounts, but I could not figure out how to get it into the shower without taking it apart, plus the tank in the shower is crimped, the way the showers are designed does not allow for gavity to aid the process, a maintenance route to add the descaler would be a gift.

It can be done by disconnecting the water feed to the shower after the gate valve in attic, then disconnecting the solenoid valve leads and supplying only the solenoid with a seperate 230v to allow water through, lie the hose down in bath to empty water from the shower tank and the now disconnected water pipe.

Then raise the shower hose above the shower unit onto its wall bracket and pour in the de-scaler in liquid form down the open water pipe in attic with a funnel until its coming out the raised shower head. This way it can be more concentrated and work overnight.

I might do it that way with my one with vinegar solution instead of removing the tank.


Not too difficult anyway for anyone with experience in electrical etc, but not an easy diy job though.

But your attic tank way seems to have worked well too.

That might work alright if you could avoid airlocks etc with the pump going. About 5 litres of the strong solution and run the shower for 20 seconds and then stop it.

With just the solenoid powered by disconnecting its own leads and connecting outside 230v, it can be poured in until its coming out the shower head which is above the shower unit height, showing the heat tank is now full. I will try it with my own one anyway and see. Its just beginning to show signs of scaling up.


Maybe actually having a very small tank in attic filled with calgon T`d into the feed pipe, switch a valve off from the main storage tank and on with the valve from the calgon mini tank would work too in areas where its a bad problem. Just have the small tank at least level with the big one in case both valves were left on.