1 establish if the taps are high or low pressure.
2 make sure the pipes supplied too whb & wc are completely free of sediment (especially living in a hard water area).
3 check if either basin or wc is connected via flexi hose (check there is no kinks in hoses)
4 check pipe work suppling both basin and wc are free from kinks ( you could pop a fitting off and see the flow from both h&c pipes,you will know straight away.
Power shower would have a separate supply pipe too basin & wc.
These are a few tricks us plumbers use for this sort of problem.
If none of the above is an issue maybe look into pumping the bathroom from the hot press which will give good pressure there but depending on a couple of factors.
Thanks for the reply.
1. No idea if taps are high or low pressure. Cistern problem suggests it doesn't really matter. Have already had the plumber back and they checked there's no pressure limiter in the cistern.
2. Am in a very soft water area. All the plumbing in the bathroom is brand new as of a week ago, so that's not the problem. Piping in the hot press is all running vertically, so also unlikely. There is some sediment in the loft tank but not above the outflow pipe.
3/4. Don't know if flexi hose means any plastic piping, or a particular type? Yes, there's lots of plastic (all of it, really). I saw the old stuff come out and the new stuff go in. No kinks.
Re: power shower, yes, confirmed it has its own wider bore supply from hot press.
The fitting company has suggested two options: a) install a pump in the hot press (they spec'd a Stuart Turner Plastic Body 1.5 Bar Pump Single Twin Impeller), b) connect mains supply to basin and wc.
A couple of problems I see -- I gather the twin pump is for pumping both hot and cold supply. But we already have a power shower which can't have another pump fitted in line with it. I know there are two cold water feeds from the hot press to the bathroom, but not aware of two separate hots for shower and basin. Would that rule out the pumped option? Not to mention that a €530 pump plus €230 labour is pretty eye-watering just to get a toilet cistern to fill faster.
What about the mains connection idea? Is there any downside (other than the obvious one, that it might not improve anything). I presume the plan would be to take a tee off the mains pipe going up to the header tank. But how do I know what flow rate I can expect? The mains connected tap in the kitchen flows a very respectable 12 litres/minute, but obviously the bathroom is 3-4 metres higher. I plan to do a test with a garden hose connected to the kitchen outlet with the other end raised to bathroom height -- not very scientific but would give an idea of the effect of the additional head?