Got a couple of suggestions from various sources yesterday that I’d be as well ditching the power shower and fitting a mains fed shower to make use of the combi boiler we have.

If I go with a thermostatic shower running off the combi, is it simply a matter of running a couple of feeds from the existing pipework for the bath into something like this – Mira concealed valve shower

The bathroom in question is upstairs, with the combi downstairs – we get about 1.0bar pressure into the house – and there’s a feeder tank for the cold water in the loft above the bathroom.

In my very limited knowledge you shoulnt need a feeder tank if you have got a combi boiler…but I am sure some one with more knowledge might be able to explain why you have one there with a combi boiler ?!?

Yes a mixer shower can work off your existing hot and cold feeds. Check the data for the showers, they should state the minimum pressure they require to work.

In theory you should install independant hot and cold feeds to the mixer valve as anyone drawing water from the same feed will affect the shower pressure and the thermostats ability to work properly. In practice you should be able to tee off the existing hot and cold feeds in your bathroom as it’s unlikely anyone will be running the taps in there while you’re in the shower.

The header tank in the loft should’ve been disconnected when you had the combi boiler installed, if it wasn’t then the cold water in your bathroom MAY be fed from it. Simple way to check this is to turn your water off at your main stop cock, if you still get water when you open the cold tap then this is the case (it shouldn’t be like that though). It may be the case that the tank is to big too get through the loft hatch so was disconnected but left in situ.

I’ll have a check, but I thought it was pretty standard to have a cold water header tank for most of the cold water in the house, and just one tap – usually the kitchen – that comes off the rising main. There used to be a small header tank in the loft alongside the biggie which fed the old boiler and hot water tank – that was all stripped out when we had the combi installed.

when you have a combi standard practice is to feed all cold water in the property from mains and not use a tank at all

most thermostatic mixer shower mixers can’t cope with a differential in pressure from mains hot to tank fed cold – you’d need to at least feed a mains cold to the shower.

mains cold and combi hot

Okay – thanks for the heads up. I’ll have to investigate further.

EDIT – just ran the taps in the bathroom, and I can hear the header tank in the loft refilling, so the cold water system has definitely been left untouched.

Would it cause a problem if the cold water feed was falling (from the mains in pipe to the loft) and the hot water was rising (from the hot feed to the bathroom)?

On a similar note, the shower I’m considering installing has removable flow regulators – if there is a problem, would removing the flow regulator for the cold inlet solve the problem?

You need to sort out the cold feed first. It should be very easy to couple up the inlet for the tank, to the outlet of the tank. Drain first obviously!

I’d always recommend a thermostatic shower valve for a combi boiler. With a mixer, if someone turns a cold tap on whilst you’re in the shower, you will get scalded, especially with low flow and pressure.

With gravity and unvented, it’s not really an issue.