Hot water problem

[portugueser]

Hi there I have a vokera linea 24 combi boiler that works fine when is in central heating mode, water temperature reads well above 70 degrees. The problem is when it is in hot water mode. No matter how high or low I turn the temperature knob it always reads around 43 degrees. When we moved in last December the hot water used to be well in the 70s. Apart from not being very hot these days the temperature also fluctuates every minute or so becoming slightly colder. To finalise the hot water pressure is quite low, sometimes practically a trickle. Has anyone got any ideas as to why this may be? Thank you very much for any suggestions.

[Ian Stirling]

My suggestion would be a scaled up secondary heat exchanger. This would explain most of the problems, the scale lets through little heat, so the boiler is modulating down to minimum, and every so often cutting out. Combis use the same heat exchanger to take the heat out of the flames for both circuits. To keep the central heating water seperate from the hot water, there is a heat exchanger between this and the hot water. If this scales up, then even at the boilers maximum temperature, little heat transfer happens. There is then a valve or something to limit flow of hot water to a minimum temperature.

Others have said that they have had success descaling the heat exchanger, with the aid of lots of descaling chemical, piping hot, and pour it through the heat exchanger, till it stops bubbling - wear eye protection.

[portugueser]