Electric shower going very hot to very cold

twopenny

Mira Sport -looks like this. Possibily 20yrs old and hardly been used in that time

http://www.berhams.co.uk/mira-sport-75kw-electric-shower

The shower runs ok on a medium setting ie small amount of heat, smallish amount of water and luke warm water.

Put it on high for a decent shower and to heat the water sufficiently in this cold weather and it goes exceptionally hot, then cold

Tonight I noticed that there was a flicker in the ceiling light and a change in the water somehow and sure enough it would go cold, run for 30secs or so then go hot again so I'm thinking that maybe the heating element/part is cutting out because it's coming through too hot.

It's as if there are 2 elements??, working ok on one but doesn't heat the winter cold from the mains - put it on 2 and it overheats and cuts out then in again.

I've thought about water pressure but told no.

I've thought about cleaning the head but already done that.

Plumber said it may be the thermostatic valve needs replacing but would need to investigate.

Can anyone advise? Is this a replacement job for a part of a whole shower? It's the only form of washing I have other than a sink.

Jeepers_Creepers

Hi t'penny.

It's very likely what you say. On high power - with both heating elements running - there isn't enough water flowing through to keep it from overheating, so the shower does what it should do and shuts down the leccy. 7.5kW is a lot of power - way more than double an electric kettle, for instance - so that's why your light 'flickers' when it goes from on to off. That's normal.

Why isn't there enough water flow? One cause is low water pressure, but you are discounting that? Does it have a 'low pressure' indicator? Is your cold kitchen tap quite nicely powerful?

Then there's two other main reasons for poor flow - or should I say, one reason but in two possible places. You have cleaned the shower head? Cool. But have you tried running the shower with the head actually removed from the hose? That will exclude it being an internally blocked head, assuming that the shower displays the same shut-off problem with its head removed. Or, what's the spray from the head rose like - nicely full and powerful? How about from the open hose end - ditto?

The other source of poor flow is the inlet filter - I think most (if not all) Mira models have them. A blocked filter would, tho', usually also show itself by a low pressure indicator. However, if you want to try it, TURN OFF THE POWER and SHUT OFF THE WATER, remove the front cover - usually one screw at the bottom and lift off - but find instructions for your specific model. ID the copper pipe coming in to the boiler, and the first thing it connects to will very likely have an extra nut head on its side, or underneath, or on top. Once you've confirmed that it is the filter, undo it and have a looksee - there will likely be a tubular gauze filter inside, possibly full of carp.

Other than that, it's likely to be a faulty pressure-switch mechanism. That's a competent DIY job.

I'm assuming that the shower doesn't have an isolating valve that's been tweaked down?

grumbler

Very odd. The flow in winter at the high setting is about the same as in summer at the low setting. That's why I don't see how the thermostatic valve can be at fault.

Exceptionally hot does indicate overheating that means insufficient flow.  Did you try running it without the shower head and  increasing the flow by turning the temperature control dial anticlockwise to the lower temperature?

It's possible, that after 20 years the heating elements overheat at the high setting because of big amount of scale inside the heating chamber. If so, it's cheaper to replace the shower.  I think descailing is possible, but not as straightforward as, say, for a kettle.

You can buy a new shower for £65 - https://www.hotukdeals.com/deals/triton-t70gsi-85-kw-electric-shower-white-ps6499-at-screwfix-free-to-collect-3640051

Lorian

Best resource for this issue here
Mira Sport Max Shower Spares | MIRA-PARENT-21 (showerdoc.com)
Probably the flow valve  -but they aren't cheap - Personally I'd replace it with a newer mira sport as then the pipe work and mains tails are already in the right places. 
if you do get it replaced check what the actual KW rating is as they make them in 8.5KW and 9.5KW versions too, they all look the same from the outside except for the label which IIRC is on the bottom. The new sports are much nicer looking.
It's not a difficult job but the person doing it needs to be competent with a spanner, compression joints and deal with mains electric in the shower zone.

twopenny

That's really helpful thank you.

When I moved in the place was barely used since built 19yrs ago but also stuff degraded through lack of use. Mouldy, dirty shower, unused water tank so I ran Milton fluid through the hose and cleaned the shower head several times

We don't get limescale here, very soft water.

I'll check the water flow as suggested tomorrow. It's good in the taps inside, even variable, but the garden tap run off the mains it is very weak (it's on the list). I'm not sure how far round to turn the stop !!!!!! tap. I did open it up some more a while back and that helped but I don't think it's fully open. Should it be?

I think I'll swap shower heads with the one I have or a cheapie from the hardware shop if it's open tomorrow. It has a fancypants head that does a thousand and one things I can't figure and a straightforward shower is all I need. See if bigger holes less gadgets helps.

I'll check the hose for kinks, maybe even put a new one on. They're cheap enough.

I do have the booklet for it somewhere. Read it lots to no avail. I've put it somewhere to check again instead of putting it away and now I can't find it. Borrowers?

But you've given me lots to try.

Had the radiators flushed today and found a leak in the immersion, then a dippsy shower. All when we get a lockdown. Joy!

FreeBear

twopenny said: Tonight I noticed that there was a flicker in the ceiling light and a change in the water somehow and sure enough it would go cold, run for 30secs or so then go hot again so I'm thinking that maybe the heating element/part is cutting out because it's coming through too hot.

Had this problem with my electric shower for a while.. Would run at the set temp for a short while, and then pulse freezing cold to darned hot. Replaced the head, and the problem disappeared. Put it down to a restriction of flow through the head.

Now have a brand new head sitting in the cupboard just in case this happens again.

Apodemus

Twopenny, in my experience, your shower's symptoms are how most electric showers eventually fail.  As mentioned above, straight replacement with a similar model is normally the easiest and cheapest option.  Personally, I "have a thing" about Mira showers, as I have battled with too many of them over the years and I have never experienced one that has lasted terribly long - but I know that plenty of people swear by them (while I only seem to swear at them! ).

Jeepers_Creepers

twopenny said:

I'll check the water flow as suggested tomorrow. It's good in the taps inside, even variable, but the garden tap run off the mains it is very weak (it's on the list). I'm not sure how far round to turn the stop !!!!!! tap. I did open it up some more a while back and that helped but I don't think it's fully open. Should it be? IT SHOULD BE NEAR FULLY OPEN. IE, OPEN IT FULLY, AND THEN CLOSE IT A HALF-TURN - THAT'LL HELP PREVENT IT SEIZING IN THE OPEN POSIITON.

YOUR INTERMAL TAPS ARE SUPPLIED BY YOUR COLD WATER TANK IN THE LOFT, SO THAT'S WHY THEY ARE RUNNING QUITE WELL. YOUR SHOWER, HOWEVER, IS RUN FROM YOUR MAINS, AS IS YOUR COLD KITCHEN TAP AND - PROBABLY-  YOUR GARDEN TAP. IF YOUR KITCHEN COLD AND GARDEN TAPS ARE POOR FLOW, THEN THAT COULD BE THE ISSUE. DOES YOUR SHOWER HAVE A 'LOW PRESSURE' WARNING LIGHT?

I think I'll swap shower heads with the one I have or a cheapie from the hardware shop if it's open tomorrow. It has a fancypants head that does a thousand and one things I can't figure and a straightforward shower is all I need. See if bigger holes less gadgets helps. WHY BUY A NEW SHOWER HEAD WHEN YOU CAN TEST YOUR EXISTING ONE BY SIMPLY REMOVING IT... IF THE OPEN HOSE END GIVES A MUCH BETTER FLOW, AND IF THE SHOWER NO LONGER CYCLES, THEN BUY A NEW HEAD. CHANCES ARE THE HOSE IS OK TOO.

I'll check the hose for kinks, maybe even put a new one on. They're cheap enough. I REFER THE RIGHT HONOURABLE LADY TO THE ANSWER I HAVE GIVEN EARLIER.

Had the radiators flushed today and found a leak in the immersion, then a dippsy shower. All when we get a lockdown. Joy! URGH!

Jeepers_Creepers

Oh, and Mira are one of these British companies that have impressed me in the past with giving fast, helpful advice. They will probably lead you through the things to check if the above doesn't help.

ShowerDoc too, as Lorian pointed out.

Mind you, with Covid they might be under-staffed.

twopenny

Well moderate sucess.

First I took the head off and ran the water through the hose. It runs at a steady temperature. Great idea.

I did try to take the fancy shower head apart but the instructions were vague so unsucessful. eased the little rubber holes with a hat pin (I can recomend those for lots of jobs), tried it on different settings and it ran more or less ok but it's still coming through hot at source then is warm by the 2ft it gets to me (I'm short)

Took a cheap basic shower head from a redundant disabled shower in bathroom that's waiting to be done and cleaned the crunchy crud from the holes (how do people do that?) and it flowed steadlily if going a little hot to warm it wasn't freezing which is a plus and I get a wider consistant spray.

I'll test it properly tonight.

Seems the adjustment for temperature is miniscule despite the large dots on the controls.

If this works I'll look at the builders merchants tomorrow for a smarter, simple head. Believe me this is pealing foil off plastic.    Supermarkets have those that have 14 ways to shower! But you can get reasonable ones for £4 in our discount DIY shop.

The comments about Mira aren't encouraging. I'm looking at an all singing, smart, flush Mira shower for the heady days when I can get someone to install a bathroom

Jeepers_Creepers

That's something at least :-)

"Seems the adjustment for temperature is miniscule despite the large dots on the controls." The LARGE control with the Hot and Cold ends usually has a nice wide range of temps. Are you saying that it has little effect - it all happens in one small position?

Just for info - the smaller low-med-high control turns on the heating elements. I'm guessing there's two elements; low is around 3kW, med is ~4.5kW and high is both on, so the full monty. The larger 'temp' control actually adjusts the amount of water coming through your shower - the faster the flow, the cooler the temp.

Set the top one to 'high' and turn the bottom one fully to cold. Switch on the baby. Are you getting quite a brisk flow, quite powerful? But, of course, it'll be cold. Now slowly advance that large control up towards hot - slowly, until you get a temp you like. Does it stay at that temp?