vaillent 435 ecotec - water temperature too low

[jericho99]

i have a vaillant 435 ecotec and a "megaflow" tank serving hot water and underfloor heating. however, the water temperature is only coming out of the taps warm - not hot - despite my increasing the top dial on the boiler with the tap (water) symbol. having spoken with someone else with a 425 ecotec, they have told me that their one has a similar issue but an engineer told them that the top dial doesn't do anything and only the bottom dial (with the radiator symbol) controls both the water temperature for the heating and the hot water from the taps. is this correct and what should i set it to - currently at 65 degrees celsius?

any ideas?

 

[D_Hailsham]

having spoken with someone else with a 425 ecotec, they have told me that their one has a similar issue but an engineer told them that the top dial doesn't do anything and only the bottom dial (with the radiator symbol) controls both the water temperature for the heating and the hot water from the taps.

That's partly correct. The top dial with the tap symbol only works if you have a combi (instant hot water) boiler. The temperature of your hot water is controlled by the Megaflow.

The bottom dial controls the water leaving the boiler. This circulates through a coil in the Megaflow and heats the contents which, obviously can never get any hotter than the water leaving the boiler.

Turn the bottom control up to 70C and check the setting of the thermostat on the Megaflow.

 

[wannocks]

Depends on the system controls. If all your controls are Vaillant and you have a VR65 or VR61 control centre both knobs will function.
If your controls are made by another company then the boiler will act as a dumb heat source and only the lower (Radiator) knob will function.