Mira Sport Max overheating

[vladman]

Hi,

I've searched on the forum, and found a few threads dealing with this, but still need a bit of assistance.

So, the shower started overheating a few weeks ago. It's quite old now, probably 7-8 years, but it's worked fine all this time (except for the whining noise, which was there from the beginning, but never seemed to affect anything, and we got used to it).

It starts off fine, and warms up, but soon an overheat light comes on, it then goes cold for between 10-30 seconds, then warms up again, is ok for a minute or so, then the light comes on again, and it repeats this cycle. As the weather's warmed up, it's now doing it more and more.

I opened it up and checked the TCO with a multimeter and it's got continuity, as I expected, as it's not cold all the time. There were some slightly encrusted bits on top of the heater tank, see pictures, not sure if this is normal.

I took off the hose and the shower head and tested it without those, suspecting limescale, and it seemed to run hot for a bit longer, but then still overheated eventually. I descaled the showerhead not that long ago, and it doesn't look bad, but I'm now descaling it again, just in case (but I don't think that's where the issue is). The hose I'm a little suspicious about, as it's a replacement, it's this one. I was thinking could it be the culprit, if the bore is slightly smaller than the original, but I'm not sure, because I've installed it in September last year, and everything was fine until the weather warmed up, and it started playing up a few weeks ago.

The water pressure seems fine, and I can't see any difference from normal.

The flow regulator seems fine too, as the flow progressively changes as you turn the main temperature dial.

Can anyone suggest what else I should try or check, in order to pinpoint the issue.

Many thanks!

 

[terryplumb]

does the temperature of the water coming out the hose ( no shower head attached )get excessively hot at any point ? if it does then the TCO is intervening as it should. does it do the same thing on higher flow ( colder ) settings

 

[vladman]

does the temperature of the water coming out the hose ( no shower head attached )get excessively hot at any point ? if it does then the TCO is intervening as it should. does it do the same thing on higher flow ( colder ) settings

Hi, thanks for your reply.

1. I'm not sure what exactly you mean by excessively (if you mean scalding, clearly-wrong-hot, then the answer is no). It just seems to get as hot as it should, on any given dial setting. In other words, the water temperature (as regulated by the dial), seems normal, but for some reason, the TCO trips frequently, like it can no longer deal with the temperatures which are normal, like it's become over-sensitive.
2. No, it's fine on colder settings, but it seems to trip sooner and sooner (I mean on less and less hot setting) the last few days, which is either to do with the weather being warmer and affecting the supply, or the fault is gradually worsening.

 

[terryplumb]

got you.although I am not fan of changing parts on old electric showers as you can buy new ones for 60 quid or so ,it looks like the cut out might be suspect ,could also be the PCB.did you remove the TCO and measure resistance or just disconnected cables and tested continuity ?

 

[vladman]

got you.although I am not fan of changing parts on old electric showers as you can buy new ones for 60 quid or so ,it looks like the cut out might be suspect ,could also be the PCB.did you remove the TCO and measure resistance or just disconnected cables and tested continuity ?

Hi, neither. I tested for continuity on the TCO still in situ (with all wires connected) with the electricity supply to the shower off, and had continuity (beeping on the multimeter).

What about the encrustations on top of the tank, is that normal?

 

[terryplumb]

not abnormal after several years for limescale to be evident .clean it by all means ,but its nowt to do with your issue. continuity through the circuit is not telling you anything. disconnect the component. what you need to establish is at what temperature does the TCO open the circuit .

 

[dilalio]

Just buy a new one.

 

[vladman]

disconnect the component. what you need to establish is at what temperature does the TCO open the circuit .

You mean completely extract it, and test it in isolation? How can I establish the cut out temperature?

 

[terryplumb]

lot of messing about ,you need a heat source ( electric clothes iron would do ) meter to measure temp and your continuity tester.but if you have the above and you like messing about to satisfy your own curiosity I can give you a diy "how to " project.

 

[muggles]

TCO. They're about £12, not worth faffing with, just change it

 

[vladman]

lot of messing about ,you need a heat source ( electric clothes iron would do ) meter to measure temp and your continuity tester.but if you have the above and you like messing about to satisfy your own curiosity I can give you a diy "how to " project.

Normally, I'd take you up on this, I like this sort of messing about, but very little time right now. But thanks again.

TCO. They're about £12, not worth faffing with, just change it

You mean change the entire shower unit?

Does it sound like it's the TCO that's the culprit here? I haven't yet heard (from reading other posts on this subject) that they can become unreliable like this, I thought they either work, or don't.

 

[dilalio]

Change the whole shower unit and move on

 

[vladman]

Muggles, I think I misunderstood, you mean you're suggesting I change the TCO, not the whole shower unit?

Dilalio, if it's something easily fixable, I prefer doing that.

 

[dilalio]

I'm confident that @muggles was advising the same as me... change the whole unit. With a new unit you'll get a guarantee, you won't with a repair.

However, we are tradesmen and you are a diyer, so the ramifications are different... I wouldn't entertain repairing an electric shower, it's not worth the grief it could cause for what is a fairly inexpensive item to replace, whereas you might be more inclined to 'give it a go' and hope a repair does the trick!

 

[muggles]

As a DIYer it might be worth spending the £12 on a TCO to see if that works before buying a new shower. As Dilalio says though, as a tradesman we take the view that new shower would at least come with a warranty and most don't advise repairing them as it can cost more than buying a new one. Essentially it depends whether you're intending to do it yourself or get someone in