Combi boiler HW variations in temperature

Hi,

Please can you advise me. I just had British Gas round to look at our Ideal ISAR HE 24 (yeah I know...) which is under contract with them. Anyway I am about to install a shower in the bathroom upstairs and I have been testing the HW output at the bathroom tap. I am noticing that the HW suppy heats up fine but after a period maybe a minute it cools and then after maybe 20 secs it heats up again. The BG guy advised me to turn up the HW supply at the boiler and to reduce the amount of flow out of the tap in order to get a more consistent HW output. Basically he was shrugging it off saying you get that with combis. I am not certain as I am sure I have had more consistent HW suppy from the Potterton / Valiants I had in previous houses. Anyway I am strongly consider using the HW output for the bath only and then installing a MIRA electric shower in its place.

Opinions anyone? Please don't simply slate Ideal as the house was installed with it before I moved in

thanks

Adam

Edit. Boiler feeds 6 Rads (which are off these days) and three HW taps. Tests were done with CH off and only one HW tap on

Is the boiler cycling on and off while you're running the tap?

Remains in D ignition mode. I am guessing that I am draining the hotplate too quickly and it has to heat another load of water = the water cools 4 a while