Vaillant heat only boiler + switched live thermostats + weather comp?

[notorious]

Sorry for coming back to an old thread, but I wanted to check how you wired up the relay? I can see how it works when the switch is on, but when the switch is off does this not mean the hot water circuit is always off?

Better late than never. Wiring is extremely simple. When the replay is off that means that Nests are allowed to steal heated water when DWH heating cycle is active. It does not mean that hot water circuit is always off.

 

[notorious]

Q. Can this forum thread approach be adapted to include a the extra Heating zone to be controlled by Vailant eBus from the VR65/VR66 ?

Why not? Try it. Calculate all heat demand situations and see if it works for you.
The Valliant native thermostat will request heat via eBus command. Once that happens, VR65/VR66 will open valve for you.

 

[bwel]

Why not? Try it. Calculate all heat demand situations and see if it works for you.
The Valliant native thermostat will request heat via eBus command. Once that happens, VR65/VR66 will open valve for you.

Sorry, I was meaning if I Use the Nest 2 - (HW, CH Rads) rather than using a Vailllant eBus Wall Thermostat, could this setup be adapted such that the VR65, could eBus control the boiler for the Nest w. CH Rads rather than be limited by the Flow Target Temp d71 and Range Rating d0 ? Given the the HW Priority is being triggered by the VR65 - Cyl Terminal - Cylinder thermostat, I’m not sure what / how the CH would be driven by the Nest2 ?

 

[notorious]

Bwel, -- VR65 can only put boiler into DHW heating mode via eBus command by receiving 240v from the outside. In that mode there's a separate register (forgot the exact number) that limits temperature during DHW heating cycle. I personally configured it for 80C. In DHW mode boiler can't go any higher than d0, which is a "global" setting. Opening valves is your own responsibility when you start boiler via RT 240v. It seems you know all the rules how the thing works.

Once you start thinking in terms of exact scenario, i.e. Nest sends 240v to valve A, valve opens and sends "I'm open" confirmation by this wire to RT, etc. etc. etc. you will answer your own question.
If unsure, write up exact scenario of what is happening step by step in as much detail and nuances as possible and I'll take a look.

 

[bwel]

@notorious Many thanks,

I was thinking that d0 (Heating Partial Load) kWh, would only effect the Heating kWh Top Limit and that d77 (Limit on cylinder charging output kWh) could be higher than d0, eg 30kWh for d77 - HW, whereas d0 could be 10kWh for the radiators ? But you have mentioned that d0 would act as a "global" setting, which I interpret would limit down in my example the HW from 30kWh to 10kWh ?

Seperate the the kWh limits of d.0 for Central Heating and d77 for Hot Water, there are also the Temp settings i.e. d71 for Target Central heating and d78 for the Hot Water. so I was thinking that neither would act as a "global" setting ?

 

[notorious]

Correct, the d0 is global.

For radiators heating mode we have one resgister to set the heating limit (same register is controlled by knob if you don't have weather compensation) and for DHW mode we have another register to set the limit. So, for radiator heating you can choose 40C and for DHW mode you can choose 80C.

 

[bwel]

Aha. I had been hoping to set d0 at a much lower Heating Partial load (10kw) with d71 at 50 degrees for my Underfloor heating. And then have the 2x 32kWh HW Cylinders charging at the full boiler rate of 30kWh (d77) with a Temp of 70 degree + (d78).

I know I can just limit the Temp d71, but I have also found that limiting the Heating Partial Load d0 to 10kWh , saves a huge amount of energy rather than leaving it on Auto or 30kWh and relaying on the boilers modulation.

 

[bwel]

Correct, the d0 is global.

For radiators heating mode we have one resgister to set the heating limit (same register is controlled by knob if you don't have weather compensation) and for DHW mode we have another register to set the limit. So, for radiator heating you can choose 40C and for DHW mode you can choose 80C.

I clarified the operation with Vaillant Technical and it is their opinion that d0 (kWh) and d77 (kWh), would operate independently i.e. if d.0 was set low eg 10kWh and d.77 was set high eg 30 kWh, then the HW d.77 would not be limited down to d.0 i.e. Not operate as a Global. However, you may well be right and the only way to tell is to try it, which I will when I have it all setup.

I'm just trying to decide if I should locate the VR65 next to my boiler downstairs and wire the eBus directly, or have it upstairs next to my Cylinder and have to wire eBus between floors (painful), but it would enable me to use the VR65 NTC, rather than CYL Cylinder Thermostat contact.

 

[Harry Bloomfield]

I'm just trying to decide if I should locate the VR65 next to my boiler downstairs and wire the eBus directly, or have it upstairs next to my Cylinder and have to wire eBus between floors (painful), but it would enable me to use the VR65 NTC, rather than CYL Cylinder Thermostat contact.

It is intended to be co-located, near cylinder and what ever port valves you have, so I would fit it there. The NTC offers much better control of the cylinder temperature too, as well as allowing you to check the temperature on the VRC display - otherwise, using the stat, it will be simple demand/no demand.

In my case, about 4m away - I had in mind to lift a bedroom floorboard to get the Ebus 2c through, but I found an easier way. I managed to fish the cable through behind the coving, from boiler to just below the airing cupboard.

 

[fezster]

Aha. I had been hoping to set d0 at a much lower Heating Partial load (10kw) with d71 at 50 degrees for my Underfloor heating. And then have the 2x 32kWh HW Cylinders charging at the full boiler rate of 30kWh (d77) with a Temp of 70 degree + (d78).

I know I can just limit the Temp d71, but I have also found that limiting the Heating Partial Load d0 to 10kWh , saves a huge amount of energy rather than leaving it on Auto or 30kWh and relaying on the boilers modulation.

D0 and D77 are configurable independently - the D77 kwh output will only be used when the boiler is instructed into DHW mode by the Vr65. The tap symbol on the front will show and the flow temperature will be boosted to 80 degrees (or whatever is set in D78) plus limited by the max temperature the hw knob on the front is set to.

 

[Yikes]

D0 and D77 are configurable independently - the D77 kwh output will only be used when the boiler is instructed into DHW mode by the Vr65. The tap symbol on the front will show and the flow temperature will be boosted to 80 degrees (or whatever is set in D78) plus limited by the max temperature the hw knob on the front is set to.

I can confirm this. I have d.0 set to 12kW and d.77 to 18kW and that is what I get before it modulates down.

Mike

 

[bwel]

I can confirm this. I have d.0 set to 12kW and d.77 to 18kW and that is what I get before it modulates down.

Mike

Perfect Mike. That’s just what I need.

 

[bwel]

Just picking up on this thread again. I’m wondering how to best address a situation with 2 Separate Domestic Heating Zones (on Nest Switched Live) as well as the HW Cyl
- DH1 - Underfloor Heating - 50 degree Target Flow - 10kw
- DH2 - Radiators Upstairs - ideally 65 degree Min Target Flow - 15-20kw load (lots of radiators).
- HW - 2x Vaillant Unistore 210L Tanks - Min 65 degree Target Flow, 20+kW

I’ve been running this with the Nest Thermostats and the VR65 as per this whole thread, but now going in to first winter, I find that as I have the Heating-Target Flow set to 60 degree so that I don’t shock / overhead and cook the Underfloor Heating screed, this is not hot enough for the HW2 Radiators to properly radiate heat.

Q1
Is there an alternative control Wiring Centre (from the VR65) that can run separate Heating Temps for DH1 (UFH) and DH2 (Radiators) ?

Q2
if not, has anybody taken an aproach to move DH2 Radiators on to the HW Control Settings and if so, how is that wired ?

Hope this all makes sense.

 

[fezster]

Underfloor heating usually has its own blending valve to separate it's flow temps from the rest of the heating system.

 

[bwel]

Underfloor heating usually has its own blending valve to separate it's flow temps from the rest of the heating system.

My mixing valve that blends Return flow with Feed Flow, is still too High temp for the floor so I need to further reduce flow to about 50, but then 50 is insufficient for the Upper floor Radiators to warm the rooms. The upstairs rads emit best at about 65 degree.

Since my last post, I’ve tried linking the Upstairs 2 Port Valve micro switch (orange) on the the CYL of the VR65 and it has now driven the Upstairs Rads as 65 (fooling DHW) and downstairs UFH at 50 on Heating).

I’ve found the limitations are however that DHW is limited in Run Duration by d.075 - Max.Charging time for domestic hot water cylinder.