Vaillant Heating Controls - Bewildering

Currently have an old Ecotec 428 (c2007) and am replacing with a new Ecotec 430.

I've been very happy with old system, nothing wrong with it but replacing / moving location as part of a bigger project.

I retrofitted weather compensation myself, its quirky but has worked fine for many years. I used the VRC430 with VR65 wiring Centre and VRT50 room stat.

Looking at new boiler, it would appear that very little if any of existing controls are compatible.

So I've bought a VRC700 with a VR70 wiring / control centre. God knows how you wire the VR70 to an existing DHW with 2 x 2 Port valves and a basic tank temperature stat????

Anyway, main question is what about the VRT50 room stat. It's now not listed as being compatible with anything apart from the Analogue Timeswitch 150?? It's not even compatible with the digital Timeswitch 160 (this appears to require an old school analogue theremostat)...totally bewildered by those combinations.

So, question is, are there options for a Vaillant eBus compatible room stat that isn't a massive box ala VR91?

Why not just keep the old setup, unless it's becoming unreliable? Do you even need 30kW? That's rather a lot...

You're right that the VRT50 can now only be used with the analogue timer, so you need either the VRC700, sensoHOME or sensoCOMFORT as your room thermostat in place of the VRT50.

Thanks for quick reply.
Why replace? 14 years old, I need to move it as part of building changes. I'm not doing this myself so as the associated costs are fairly high (lots of pipework / hot water tank move) I thought I'd bite the bullet with a new boiler at same time. Plus I've convinced myself that newer boiler won't have same quirks (the current one hates switching between Heating and DHW - doesn't like the sudden flow/ return temp difference, goes into a wait state and can take up to 25 mins to sort itself out again). I read that this was a well known thing with my era of boiler.

House is on the large side & detached. Probably don't need 30 KW but the modulation is pretty good on Vaillant stuff.

I've already instructed my plumber to install but I know full well that he's not likely to be up to speed on the weather comp setup so I was planing on doing that bit myself - as I had done with existing system. Looks like I should have thought this through in more detail! I've been through the 3 manuals - boiler / VRC700 and VR70. They are unbelievably obtuse. I understand the increased capabilities of VR70 but can't believe how cryptic the required config details are just to get a simple single zone system in place.

I'll ask my plumber but fully expect them not to know / will revert to bog standard external timer driven controls then I'll explore the SensoComfort requirements at leisure.

Can the SensoComfort (wireless) be used as a portable / freestanding device so that I don't need to wall mount it? My current VRT50 on the eBus is located where there's not enough wall space for larger unit and getting a new cable run in for new eBus would be a significant undertaking.

Thanks for your help.

exocet said:

same quirks (the current one hates switching between Heating and DHW - doesn't like the sudden flow/ return temp difference, goes into a wait state and can take up to 25 mins to sort itself out again). I read that this was a well known thing with my era of boiler.

Click to expand...

Could be a symptom of it being oversized, which an even more powerful boiler won't fix, or a poorly set up auto bypass, or both. Either way you'd be much better off getting a boiler which is properly sized for your house rather than guessing. As a rough rule of thumb we say 1kW per radiator but a proper heat loss calculation can be done on www.heat-engineer.com. An oversized boiler will be inefficient, even with the modulation, and a lower max output also means a lower minimum which further benefits efficiency.

Yes, the sensoCOMFORT RF is purely battery powered so can be positioned in a different location, although it doesn't come with a table stand, just a wall bracket.

I did look into the sizing, as you say better to have boiler in the right range. The odd thing is that the next one down in size (24 KW) appears to have a minimum output of 7.6 KW which is higher than that quoted for the 30KW unit which quotes 7.2KW? I've got 20 radiators with separate 22mm loops feeding different floors in the house (4 Floors). DHW is via a 210 Ltr Megaflow that has a 25KW heating coil so given choice between 24KW and 30KW with the 24KW apparently not able to modulate down as low, I've gone with the 30KW. The occasional issue that I have with the current system does appear to be well known with the era of ecotec that I have. I run the unit in condensing mode, the flow temps are less than 56 deg most of the time). However when switching to heat hot water, the return temp drops quickly as it circulates through the cold DHW coil, the boiler increases output for about 20 seconds but then when the return temp still doesn't increase fast enough it decides that there must be an issue (error code is linked to too wide a temp differential between flow and return). It then goes into some kind of anti-cycling mode for up to 25 minutes before it decides to play ball - ramping up the output just as high as before but this time accepting that the return temp will take a little longer to reach an acceptable level. The valves feeding the DHW heating coil are wide open, pipework is in 22mm so unrestricted flow). If I'm in a hurry for hot water, I can simply power reset the boiler as soon as it's gone into first anti-cyling mode and all is good. When running in central heating mode only, there's no issues with cycling, it can run for many hours at a time appearing to regulate itself quite happily according to demand.

Looks like i'll have to go down the SensoComfort route but searching on the requirements for integration, it appears to stipulate using a VR66/2 (I'm guessing that's a recent 2nd revision to the VR66) - however, many outlets don't state whether they are selling the Rev 2 and Vaillant have used the same part number 0020135785 for both Rev.1 and Rev.2 units which doesn't help matters.

Thanks again for your help, much appreciated.