I'll be upfront with you from the start. As you know, I am a plumber, so I'm writing this from a plumber's point of view. However, I will try my best to give you some good balanced advice.
Do the electrics need to be altered in any way?If it is a straight swap where no alterations are needed to the existing electrics then a plumber can do the work. By 'no alterations' we mean that the electrics feeding the shower don't need extending, upgrading or changing. If they do then you need to get a qualified electrician in.
Part P (Building Regulations) below states that if any additions or alterations are made to an electrical circuit in a bathroom then the work is notifiable:
Make sure you buy a replacement shower that is suitableA word of warning before you go out and buy a replacement shower. Make sure you know the KW rating of your old shower. If your existing shower is 8.5kw then I would recommend replacing it with another 8.5kw model. If your existing shower is 8.5kw then it may be that you have 6mm electrical cable supplying it. Anything over 8.5kw should in most circumstances have 10mm cable. By choosing a shower of equal rating you should also avoid having to upgrade your fuse at your consumer unit.
What if I can't get an identical replacement or I want a different model?Companies like Mira and Triton have made it as easy as possible to replace an existing shower without having to alter the electrics or water supply. Models like the Triton Fast-Fit and Mira Multi Fit have adaptable and multiple cable and pipe entry points. The manufacturer websites also give plenty of guidance as to which new models are suitable to replace existing models.
Do I need an RCD fitted?A Residual Current Device (RCD) is a safety device that switches off electricity automatically if there is an electrical fault. As an RCD is much more sensitive than a normal fuse or circuit breaker it cuts off the electricity supply much quicker. It therefore provides additional protection against electrical shock.
Although it is not a legal requirement to install an RCD on an existing shower circuit, I do strongly advise my customers to get one fitted by an electrician. It gives you that extra safety and peace of mind.
if you just want a replacement shower in the same location as the old one, then a plumber who is competent with electrics is good for the job. On the other hand, an electrician who is competent to do the plumbing can also do the job. Having said that, I have known a few electricians over the years and most of them want nothing to do with plumbing work.
Although I am not a qualified electrician, I do know how to carry out the basic electrical tests and checks required. If there is any doubt in my mind about the safety of the electrical side of the installation then I get a qualified electrician in to check it out and make any amendments necessary. It most definitely is not worth taking risks where water and electricity are concerned.