Vaillant Combi Boiler - Water temperature fluctuates

[TheBigFC]

I have moved into a house with a Vaillant combi boiler fitted, unfortunately I can't find anything telling me what model it is.

The hot water dial is turned to full yet when running the water from any of the taps in the house the temperature of the water fluctuates from hot to luke warm (not nice when having a shower). Even when the water is at its hottest it still isn't as warm as you would expect, especially compared to the radiator temperatures.

Any suggestions?

 

[ChrisR]

It's usually due to sludge/obstruction in the tap hot water heat exchanger.

Does the boiler have an LCD display (Turbomax plus)
or has it got a black inner panel with green knobs (Turbomax)
or has it two square gauges and a metal door hingeing at the side
or has it got a "stripe" panel in the middle

 

[TheBigFC]

Metal door hinging at the bottom, with an LCD display for the temperature only. 2 knobs on the left hand side for hot water and the central heating. Timer is a Timeswitch 110...