I'll pay money for constant hot water temperature......

Throttle back your water. ie only open a tap halfway; is your water now at a constant temp?
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The water from the hot taps is hotter but the temperature still fluctuates (from hot to very hot). On the technical blurb for my boiler is says that the maximum inlet pressure is 6.0 bar - is there any simple way I can find out what the water pressure coming into the boiler is?
Very simple, phone your water supplier. They'll know all about high pressure areas cos that's where their leaks will be worst. But if your wp is high and the combi's new, there must be a heck of an obstruction for you to get very hot water when the tap's full open.

To measure your hot water flow rate, time the filling of a calibrated bucket. Many have litre marks down the side.
Cheers for the advice! Would fitting a combi-compatible thermostatic shower head onto the shower prevent hot water temperature fluctuations?
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A thermostatic valve will help but it won't do miracles, if the inlet water gets cold, the valve won't make it hot... :eek:

Modern combis are normally quite good at regulating the HW temp as long as the flow rate remains constant.

As it's been suggested, you first need to figure out your flow rate with a bucket. You could have 20l/min even with the tap half open, twice what a combi can handle...
OK.....the flow rate of water from a cold tap is 25L/min. However I've noticed that when a hot tap is tunred on full the combi boiler seems to ignite, then turn off, ignite, then turn off so it seems that the water temperature fluctuations are caused by the combi not being 'on'. Could this be a thermostate problem? :confused:
Your combi is overheating :rolleyes:

It can probably only handle 10 to 12L/min at 35°C rise (check the spec), you're asking for over twice as much.

Reduce the flow rate until you get a stable temperature.

You can install a pressure reducing valve on your mains supply to avoid exceeding your combi max flow rate.
Many thanks for the advice - hopefully one step closer to a normal shower!!!

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