CH & HW system upgrading

[HarryM1BYT]

I wonder if anyone might have some familiarity with Vaillant heating systems?


I had a new EcoTec 418 Pure installed last March, on my open vented system to then find it only had one boiler output temperature setting. Wanting the HW hot, I had to set it to 75C, but since then for CH it has tended to run flat out then off, with not much modulation - so not a very efficient way to run. This was using a Sunvic SDM 1901 three port, separate timeclock and mechanical room and cylinder stats.



This past week, I have ripped out timeclock, both stats and replaced them with a new fancy Vaillant control system. A VR65 (Control Unit) linked to the boiler via an ebus and a VRC 407F, which connects wirelessly to the boiler module and module also connect wirelessly to an outdoor sensor, so the boiler output can auto-compensate for anticipated heat loss. It is also supposed to allow HW temperature to be set independent of CW. 407 is a combined LCD display, room temperature sensor, clock and has all the means to adjust the setup.



CH is working spot on, boiler output is now modulating its output perfectly as it is supposed to and generally its output temperature is well within the condensing range.


I have set HW to 70c via the 407, but it never achieves it, the best it seems able to manage is around 50C - it just never gets there so demand never cuts off.


I have tried adjusting the boilers settings via its own LCD, to set it so it knows it is working with a mid- position 3-port, that allowed it to enable CH setting and HW setting for output temperatures, I set both to max. 75C CH and 60C HW, but HW cylinder still only manages around 50C.


Odd that the 407 allows 70C for HW, but the boiler HW max flow is only allowed to be set at a max of 60C.. Unless this particular setting in the boiler was only intended for when it was a combi version of the boiler?



I have three times emailed Vaillant to ask if the VR65 + VRC407F + ECOfit 418 + SDM 1901 were compatible with each other, before buying - they replied three times saying nothing more than that my VR65 + VRC470F were superseded by the VR66 + VRC700. They gave no clues about any possible compatibility issues at all.


When the HW desired is set higher than the around 50C it can achieve, the boiler will be cycling constantly trying to achieve it. So HW boost never switches off. Adjust the desired to somewhere less than 50C and boost manages it and turns off just fine, but we want hotter HW than nearly 50C.