Vaillant Combi boiler with Unistor

14 Apr 2009
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United Kingdom

I have an existing Vaillant ecotec plus 824 and needed to extend my heating/water system as I have two cottages next to each other and we are converting them into one. After going through countless plumbers, that all told me different things, I settled on one that told me not to go through the expense of a new boiler (one I have is only just two years old) yet and just to add a unistor cylinder and divert the boiler to a sink allowing the cylinder to serve the rest of the hot water as the boiler is big enough to serve the house as a whole. I believe the system is now an S plan.

I wanted to stick with Vaillant parts as to me that makes sense and asked to have the VRT 360f installed. I was told by my plumber/electrician that they would need to use a VR 65 control centre. Anyway long story short they couldn't because it won't work with a combi and they couldn't wire the VRT 36f without the VR65 and so on.

I have been left in `limbo` without a room stat connected and no wireless controls as they have told me they need to source an alternative control, this was 3 weeks ago. I have not yet paid them and don't intend to untill it is sorted.

Is it normal practice to run a combi bolier as, essentially, a system boiler? has anyone else done this? And if so what controls did you use? Or has it been `bodged`

Many thanks

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your combi can work on an S plan no problem. The Unistor has a standard cylinder stat fitted so it can be used like any cylinder. This system could be wired up quite easily with controls from any DIY store or merchant, don't know what the problem is. Certainly won't work with vaillant ebus controls though.
Haven't come across an electrician yet that can wire up a ch system, apologies to any that can.
Hi mickyg,

Exactly my point I just don't get what the issue is?? I have even suggested controls to use but they say `we will get back to you` and never do! You would think that they would want my money!?!

I'm reasonably handy with electrics but not sure on wiring up a stat to this boiler, if anyone could pass on any hints on how to do it I would be very grateful.

Many thanks,
if you google s-plan wiring you should be able to find a diagram that will show how to wire up controls. The boiler needs a permanent Live, Neutral and Earth, then the two orange wires from the motorised valves need connecting to No.4 terminal on the boiler.
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The problem sounds like they don't want to 'throw away' the Vaillant controls.

As micky says, if you do this, then all will be ok.
don't have that particular manual but do have the auroSTOR (twin coil solar) and in the back is all the info for wiring boiler / cylinder via a VR or a standard wiring box
try ringing Rochester and asking for a copy of the cylinder manual

01634 292300
The problem is that the boiler thinks it is a combi and therefore won't allow the ebus controls to work as if it were a heat only boiler.

So the easy way is to use standard controls across pins 3 & 4 as suggested.

The difficult way is to convert your boiler back to a system boiler, because I think the electronics are identical. There is a coding plug or something in the loom that tells the PCB what it is fitted to. If Rochester are feeling helpful, they may be able to tell you how a Vaillant ecoTEC knows it is a combi or a system boiler........

If you can find this out then you can ebus control it....!
Many, many thanks for this very helpful. I'm going to give the guys a couple more weeks to sort it out then I will write to them saying that I will get it sorted.

Very useful and helpful forum

Many thanks,


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