Connecting ESBE valve to Vaillant ecoTech Plus for UFH mixing

[ricardo100671]

I have followed this advice, from Urban Plumbers, and fitted an ESBE motorised valve to my manifold as mixing valve for UFH, but not sure what I need in order to connect it to my Vaillant ecoTech Plus. It is a single zone setup with 1 sensoHome Stat and weather compensate.

Thanks in advance for any help.
 

 

[JohnMo]

Do you have a mixed system, radiators and UFH? He is describing a two zone system, you have a single zone. So there are radiators and UFH, each can run independently of the other. If you have just UFH do you need to mix down?

 

Are you setup to up to run priority domestic hot water?

 

Do you have the Vaillant wiring centre he mentions?

Edited August 27 by JohnMo

[ricardo100671]

On 27/08/2025 at 08:08, JohnMo said:

Do you have a mixed system, radiators and UFH? He is describing a two zone system, you have a single zone. So there are radiators and UFH, each can run independently of the other. If you have just UFH do you need to mix down?

 

Are you setup to up to run priority domestic hot water?

 

Do you have the Vaillant wiring centre he mentions?

Thanks @JohnMo. 

Yes I have mixed system. My rads need to run at 50degC and UFH at 28. Did not get the wiring centre yet as not sure which one to get, of if I even need one, given my simple system. If I do get one,

I assume would treat the mix valve like any other actuator, but what is confusing to me is that, my understanding is that the actuator is controlled bassed on the related connected stat, so that the actuator is closed when the stat reached setpoint, but for the mixer valve there is no stat. Does that mean I should have fitted a floor sensor stat and that is what is paired with the valve at the wiring center ?
 

[JohnMo]

53 minutes ago, ricardo100671 said:

assume would treat the mix valve like any other actuator

Not really you should have a 3 point actuator, so it will have power to move one direction and power to move another, plus it will need to read flow temperature 

[JohnMo]

This video shows you what you need and how it works 

https://youtu.be/iHRdlLeqm7Q?si=R62xc2Xma48Hjr-U

 

[ricardo100671]

On 04/09/2025 at 09:12, JohnMo said:

This video shows you what you need and how it works 

https://youtu.be/iHRdlLeqm7Q?si=R62xc2Xma48Hjr-U

 

That is great ! Thank you. Just a couple questions after watching that
- At around 1:00 he seems to describes how the valve maintains temperature by pushing the flow out to the return, but the at 1:40 he seems to state just the oposite that cool water is coming in to the valve from the return, which is how I thought mixers valves actually work ?
- Do I need to have two circuits, if I only have a single zone, my thinking was that the ESBE will just always keep the UFH set at a relative temp to the RADS. So system flow would be 50 and I would restricit the ESBE set point so the UFH flow is only 26. Then the system should remain balanced if. i.e. if boiler lowers or raises flow temp depending on weather compensate rads/UHF flows should remain constant at same ratio. (hope that makes sence)
- Why would I want to turn the system off if outside temperature reaches certain temperature ? I that not the job of the Stat, based on inside temperature ?

This is how my system was plumbed. Aside from the controll centre and pipe sensors, I dare ask how wrong it is and what else I am missing on it to get it working ?



Thanks again for all the advise 
 

[JohnMo]

Do you need the tee and join between flow and return between the two manifolds?

 

You will need two circuits, but they are going to stay on all the time. You will need two different WC curves one for the radiators and one for UFH. If you applied the same curve to both circuits it wouldn't work. Mainly because the design day flow temps are different by a big margin.

[ricardo100671]

I did that based on the Urban Plumber's vid you posted above. You can see right at the start his manifold setup seems to tee off both flow and returns.

If I need two circuits would I need 1 or more valves on this pipework somewhere ?

[JohnMo]

So is the left manifold feeding the radiators? The right the UFH? The tee being your mixing valve?

[SimonD]

1 hour ago, ricardo100671 said:

I did that based on the Urban Plumber's vid you posted above. You can see right at the start his manifold setup seems to tee off both flow and returns.

If I need two circuits would I need 1 or more valves on this pipework somewhere ?

 

You haven't really followed what was done in that video. On your system you need:

 

- Vaillant wiring centre to wire in the mixer and additional sensors - really you want the SensoComfort together with the VR71 wiring centre and this has up to three outputs for ESBE mixers and has the inputs for several system temperature sensors that you're going to need as well as the DHW cylinder sensor and pump control output for UFH.

- you need a pump on the UFH side of your circuit between the mixer and ufh manifold. This is because as you have a gas boiler you need different flow rates between radiator circuit and UFH circuit because you want a delta T of 20 for rads and delta T of lets say 7 for arguments sake on the UFH but once the flow is outside of the UFH circuit you want a delta T of 20 between boiler flow and return.

- you need temperature sensors on your pipework so that the controls can differentiate between the temps of the radiator circuit and the UFH circuit (and provide input to the ESBE mixer).

 

In the video, the first thing he points out is the close couple tee arrangement below the boiler which is to provide hydraulic separation between the two circuits - you really must have this in your system for it to work correctly

 

 

[ricardo100671]

2 hours ago, JohnMo said:

So is the left manifold feeding the radiators? The right the UFH? The tee being your mixing valve?

Yes Correct

[ricardo100671]

2 hours ago, SimonD said:

Thanks @SimonD

In response to your points
- Vaillant wiring centre to wire in the mixer ....
Yes I have now bought the VR71, which I think may be overkill, I think VR70 would have been enough, and have a sensoComfort and weather compensate connected already

 

- You need a pump on the UFH ... 
Based on UP other vids about caldulating heads etc. I figured my system is low enough to be handled adequately  by the boiler pump, since it is all ground floor and all rads are fed from manifold all with smooth curves. As for the flow rates, Can't understand why this can't be managed by flow restrictors on the manifold. I could check the deltas on the return to ensure I get correct flow for every loop, incl. rads. Any reason this would not work ?

- You need temperature sensors on your pipework so that ...
I see, yes I will have this as part of the VR71, but, I wonder, is this why I need the hydraulic separation .. I did note his mention on this, but did not elaborate and I guess I did not quite understand. If it is about sensing different temps for each circuit,  would a sensor on flow before each manifold input not achieve this ?

 

 

2 hours ago, SimonD said:

You haven't really followed what was done in that video. On your system you need:

 

- Vaillant wiring centre to wire in the mixer and additional sensors - really you want the SensoComfort together with the VR71 wiring centre and this has up to three outputs for ESBE mixers and has the inputs for several system temperature sensors that you're going to need as well as the DHW cylinder sensor and pump control output for UFH.

- you need a pump on the UFH side of your circuit between the mixer and ufh manifold. This is because as you have a gas boiler you need different flow rates between radiator circuit and UFH circuit because you want a delta T of 20 for rads and delta T of lets say 7 for arguments sake on the UFH but once the flow is outside of the UFH circuit you want a delta T of 20 between boiler flow and return.

- you need temperature sensors on your pipework so that the controls can differentiate between the temps of the radiator circuit and the UFH circuit (and provide input to the ESBE mixer).

 

In the video, the first thing he points out is the close couple tee arrangement below the boiler which is to provide hydraulic separation between the two circuits - you really must have this in your system for it to work correctly

 

 

 

[JohnMo]

The first video, had two distinct zones, UFH and radiators, which is different from you are doing. The primary circuit was at the boiler with secondary circuits for radiators and UFH each requires it's own pump.

 

You will be running both areas (UFH and rads) on unison, so you really don't need hydration seperation to keep boiler happy.

 

Whether you need dT20 to keep boiler on side with a max flow temperature of 50 is debatable, and something that can be set anyway. Trouble with dT20 thing, is when you are running WC and it's mild your flow temp could be 30 for the radiators, so dT 4 or 5 works, dT20 definitely doesn't as return temp is lower than room temperature.

 

Discussion here on dT settings 

 

 

[SimonD]

23 hours ago, ricardo100671 said:

I figured my system is low enough to be handled adequately  by the boiler pump, since it is all ground floor and all rads are fed from manifold all with smooth curves. As for the flow rates, Can't understand why this can't be managed by flow restrictors on the manifold. I could check the deltas on the return to ensure I get correct flow for every loop, incl. rads. Any reason this would not work ?

 

Yes, the boiler pump is almost certainly able to deal with the index circuit press drop. The reason you need the hydraulic separation is that your flow rates will be different when you have a different Delta T - the difference between flow temperature and return temperatue. So even if you ran your rads and underfloor heating at a Delta T of 7 (7 degrees temperature difference between flow and return) for example, your boiler still wants to ideally see 20. At a Delta 7T you will have almost 3x the flow rate through the system than at Delta 20T and this will cause problems at the boiler side because of the way gas boilers run - typically if the Delta T across the boiler becomes too small it will tend to short cycle. This change in flow rate between what the boiler wants to see and the emitter system will need the addition of a pump post hydraulic separation.

 

A case in point about boiler Delta T is with my current gas boiler. On Opentherm this is set to run at a maximum flow temperature of 53C. On very cold days, I have a typical return temperature of 37C (even though I have a perfect Delta T of 20 across both of my system manifolds - make of that what you will) - I can't get the settings to work any lower on this boiler. When the return temperature at the boiler reaches 41-42C the boiler begins to short cycle with a max flow temperature of 53C. But it will continue to run fine if I increase the max flow temperature to 55 or 60C. So my boiler just will not run well when the Delta T gets to minimum 11-12C. At minimum 16 it will run for long periods of time.

 

IMHO it isn't worth trying to make a gas boiler run like a heat pump, they are different technologies and thus need to be treated that way.

 

23 hours ago, ricardo100671 said:

I think VR70 would have been enough

 

No, it wouldn't because it doesn't have the inputs and outputs for temperature sensors and electronic circuit mixing which you need for the ESBE, unless you use an ESBE product that has its own weather comp/room load compensation controls.

 

 

 

 

 

 

 

[marshian]

2 hours ago, SimonD said:

IMHO it isn't worth trying to make a gas boiler run like a heat pump, they are different technologies and thus need to be treated that way

It’s absolutely possible to run a gas boiler like a heat pump but you need the right boiler that can cope with narrow deltas between flow and return at the boiler.

 

my Viessmann has no issues when doing CH with a flow temp of 30 deg and having a return of 23 on CH it’ll tun for 20 to 40 mins at a time without cycling

 

when doing HW flow of 64 and a return of 57 it will also not cycle and will do the water heating in one hit (obv delta is wider at the start of water heating and narrows as the tank heats up)

 

 

 

[JohnMo]

5 hours ago, SimonD said:

IMHO it isn't worth trying to make a gas boiler run like a heat pump

Unless it's an Atag (and others) then it runs just like a heat pump, like it or not. Up to about 40, has a dT 4 or 5, dT progressively widens but not be much. Doing DHW with ASHP cylinder and flow temp cap of 60 degs, would slowly ramp up flow temp over about 15 to 20 mins, exactly the same as heat pump and settle at a 4 to 5 Deg dT. At the end of the cycle dT would start to drop when it hit 60 degs, going down to about 3.

 

Both were done with zero cycling.

 

Built for the UK market, and simple S and Y plan you have 20dT and that's about it.  Modern boiler built really for Europe (Atag Viessmann etc), W and X plan and weather compensation, you get a boiler that runs just like a heat pump.

[SimonD]

3 hours ago, marshian said:

Viessmann

 

38 minutes ago, JohnMo said:

Viessmann

 

I kind of knew I'd get some kickback from what I said and I'm not surprised from whom 😉

 

I'm an approved Viessmann installer so I'm fairly familiar with how they work and most of my installations with Viessmanns are with unvented cylinders and PDHW bla bla bla.... and I don't treat them like a heat pump. CH and DHW need to be considered differently in both design and commissioning and it's not uncommon to see lower DTs when in DHW mode in PDHW but then flow temperatures are much higher

 

.and @JohnMo you have repeatedly talked about the problems you had getting your ATAG to run as you wished it to which wasn't as it was out of the box and it didn't run like a heat pump...e.g.

 

On 17/08/2025 at 12:21, JohnMo said:

Been there done that with UFH biggest disaster of all the options I tried and tested (Atag boiler)

 

On 17/08/2025 at 15:47, JohnMo said:

My final version of gas powered UFH, wasn't pure weather compensation as boiler just wouldn't modulate down far enough at low temperature and cycled too much to be efficient.

Edited September 7 by SimonD

[marshian]

1 minute ago, SimonD said:

I kind of knew I'd get some kic back from what I said and I'm not surprised from whom 😉

 

I'm an approved Viessmann installer so I'm fairly familiar with how they work and most of my installations with Viessmanns are with unvented cylinders and PDHW bla bla bla.... and I don't treat them like a heat pump. CH and DHW need to be considered differently in both design and commissioning and it's not uncommon to see lower DTs when in DHW mode in PDHW but then flow temperatures are much higher

I didn’t regard it as kick back - more that “most of the cases you are right trying to make a gas boiler run like a heat pump isn’t going to make the boiler happy” But it’s not a hard and fast rule…….

 

If people do get a boiler that can run lower temps than most and has a high modulation then it can be quite happy “pretending” to be a heat pump in terms of delivery of heat to the house ufh or rad circuits.

 

it can also go back to not “pretending to be a heat pump” when asked to do HW 😉

 

I’m sure other boilers are equally capable of doing the same but a few manufacturers are lagging behind and they need to up their game

 

Viessmann however need to do a better job of writing their installation and operating manuals 😉

[JohnMo]

39 minutes ago, SimonD said:

and @JohnMo you have repeatedly talked about the problems you had getting your ATAG to run as you wished it to which wasn't as it was out of the box and it didn't run like a heat pump...e.g.

 

On 17/08/2025 at 12:21, JohnMo said:

Been there done that with UFH biggest disaster of all the options I tried and tested (Atag boiler)

Nothing like out of context quotes, to make a point - that discussion was about room compensation and UFH, you said it was needed and I stated I tried it and it didn't work - so not relevant to this discussion.

 

41 minutes ago, SimonD said:

pure weather compensation as boiler just wouldn't modulate down far enough at low temperature and cycled too much to be efficient.

In that case, boiler at min flow temp kicked out over 9kW, I only need around 3kW at max demand, so no surprise it didn't work.