Vaillant eco tec pro 428 with VR66, VRT350 (ebus) and Vr10

4 Jan 2018
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United Kingdom
I have an eco tec 428 boiler running in sealed system with VR66 VRT350 wired and A VR10 NTC sensor, System runs well in central heating mode but i cannot call DHW VRT timer is set so that DHW is on, VRT350 shows hot water temp in installer menu and boiler off during DHW demand time and HEATING during CH time, i know that the VRT350 is good and ebus wiring is good (twisted pair screened cable) measuring volts across CH1 i see 230VAC in CH mode but i see nothing across DHW on, i have swapped out the VR66 without any success hot water tank is Vaillant unistore VR10 in dry pocket two 2 port valves

Can anyone give some suggestion as to a possible cure
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I have No idea, what do i do to find and read this value
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Ok, Thanks but this will have to wait untill the morning, Am i correct in thinking i need to set D70 to 0??


  • VR66 manual page 7.jpg
    VR66 manual page 7.jpg
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Put it on 1 to make sure you have everything connected properly, both valves should open and close on demand, if they do then make sure you have the valves connected to the correct position in the vr66 before selecting hot water priority (0) in d70.
Last edited:
I looked at D70, it was set to 0 i reset it to 2 then back to 1 the DHT came on and the system is now working well.

Thanks for your help.

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