This is a common question and i have come across some horrific incidences of things going wrong! Well said on the caution on the other posts here by the way - cudos to you people and you are absolutely right!
Argos knock out some cheap and occasionally some alright showers but you are way better off going to a merchants.
Stick with these brands:
thats it really!
Avoid Gainsborough and Aqualisa like the plague. These last a couple of years and the guts leak water and rot isnide very badly. Just trust me - Mira and Triton, although nothing is infallable, are as close to bulletproof in the shower world as you are going to get.
Ok first of all yes you COULD just swap it straight over and it will by all appearences work.
However if the kilowatt (power rating) of your shower is too high for the cable the cable will melt and if you are lucky trip your board out, worse case catch fire or electrocute you or even both!
I have seen it so many times where peple upgrade to what appears to be a bargain 10.5kw shower and spanner it on to what used to be a 7kw shower and the cable is just not big enough and its black inside when you go to see whats happened!
One case the wire melted, and came into contact with the metal bath they were standing in and fried them like a cajun catfish.
You need an electrician or someone who is electrically qualified to look for the following criteria:
Distance betwen board and shower and the showers power rating, and gauge the thickness of cable required to take the load due to resistance and not melt/get hot.
Earth Bonding - is there any?!
RCD protection. If its the old wired fuses you need to upgrade to RCD protection in some form or another, be it a sub-board or just upgrading your board.
Isolating switch - is there a pull cord or switch outside the room or other safe are and the switch up to standard and in the right safe zone?
And is it a dedicated circuit? I have seen loads spannered into the plug socket ring and after a while of use keeps blowing the board and melting all the plug ring circuit wiring in the house leading up to it!
To re-itterate what the others say - its just not worth it!
I have been to jobs with what seems to be a perfect straight swap and still get the sparky in to check it. 9 times out of 10 its fine, but for that 1, he is worth every penny for the other 9 he has checked ut for piece of mind. Better than frying a kid and ending up in the press or TV.
Good merchants are WATERMARK and PLUMBASE. Miras do cost a bit more but for the sake of £40 you get piece of mind, something that looks smart, and will last twice as long if not three times! My old boss fitted a MIRA sport in my parents house 17 years ago, and there isnt a mark on it or even inside and it gets used twice every day. A little 7kw. You just dont get that with any other manufacturer par for par. Bullet-proof!
Good luck and hope it works out ok.
Plumbing and Heating engineer (CORGI now GAS SAFE) for 12 years and love it! Just seriously dont mess with electricity, less than an amp can stop your heart and 3 is more than enough to pin you in spazm to an appliance!
If you have a combi, swap your bath taps for a thermostatic bath shower mixer! Way powerfuller and safer. A MIRA EXTRA bath/shower or a MIRA EXCEL bath/shower mixer. Your family will be well happy, combi power kicks **** over electric any day!
Nice to have a leccy back up tho incase boiler goes down.