Vaillant VR65: change from unvented cylinder stat to VR10?

[jimalad]

I've recently had the following installed...

ecoTEC Plus 624 System, VR65, VRC430 & outside temp sensor, Telford Tempest solar unvented cylinder + solar collector/controller/pump.

My installer has used a traditional thermostat mounted at the level of the boiler loading coil to provide feedback to the VR65 that the water is up to temperature.

I've noticed that when the boiler heats the domestic hot water, the loading circuit flow temperature is a flat 80 degrees celcius. I know that the boiler is capable of modulating its burn and wonder if I can swap the thermostat for a VR10 temperature probe instead. They seem inexpensive (£10). It could be inserted into the same cylinder dry pocket that previously held the thermostat. If this change were to be made then I presume that I'd then get the cylinder temperature reported on the VRC430, I'd be able to set the DHW demand temperature via the VRC430 and I've also read in various posts that there might be a DHW 'boost' feature unlocked, but maybe that's not the case? Essentially I'm interested in increasing the system efficiency and the way I have it set up right now just seems illogical to me as there's valuable information about cylinder water temperature that the control system cannot make use of.

I've read in this thread that a VR10 has been installed with VR65 on a non-Vaillant cylinder. In the same posting though, I understand that they still employ a secondary over-temperature fail-safe mechanism that uses a traditional thermostat that shuts the loading coil valve in case over over-temperature. Is this really necessary? In this thread, there's discussion about whether the VR10 feedback method meets regs in the UK. Is the fail-safe control of the valve a way of clarifying this grey area, or would a pure Vaillant VR10 / Unistor installation still be fitted with this kind of failsafe as best practice?

I'm going to get my installer back to make this change, if it's turns out that it's sensible. I want to be super-clear to them though about the spec so there's no misunderstandings. Any thoughts?

James

 

[Agile]

I would say ask your installer but by asking here it seems you may not trust him to properly advise you.

There can be a level of debate but expressed simply, if you dont have a Vaillant boiler/cylinder which are approved as a COMBINATION then you have to have the motorised valve on the heat coil of your cylinder as the fail safe shut off in case anything went wrong.

Hopefully you installer is qualified to fit unventeds and will have already fitted that motor valve?

Tony

 

[Beerlover]

Remember the GIUSR states that the MIs are paramount and the Vantage systems never needed a two port fitted

 

[dfaz]

the position that the vr10 sensor fits into the unistor cylinder makes the control temperature acurate for the unistor only,installing it into another cylinder may not control the temperature correctly and could create a dangerouse overheat situation,the vr65 prevents overheat situations when using all vaillant components as there is no resetable overheat fitted.you could wire in the existing overheat to kill power to the zone valve to give overheat protection but how well it would controll the hw temperature remains to be seen.

 

[jimalad]

Thanks for the replies. Yes, the motor valve is already fitted and as I already have the thermostat, I guess wiring this into a failsafe interlock wouldn't be too hard. I will ask my installer and see what they say.

James

 

[Agile]

As long as you keep the motor valve and its wired into the boiler interlock then you can fit the Vaillant sensor on your cylinder.

Tony

 

[cmhicks]

I've recently had the following installed...

ecoTEC Plus 624 System, VR65, VRC430 & outside temp sensor, Telford Tempest solar unvented cylinder + solar collector/controller/pump.

Hi James,

I am just about to have a very similar system installed, including a Vaillant System boiler (the 630 in my case). However, my installer has recommended Honeywell controls, rather than the Vaillant ones - his implication seemed to be that English people are too thick to understand the German controller!

Anyway, I was wondering how you're getting on with the system - especially the Vaillant 430 controller - and also why you needed a VR65, and did not install the VR68 Solar Controller.

Thanks in advance,

Christopher
==
PS feel free to reply offline if you prefer: cmh21 at cam dot ac dot uk.

 

[jimalad]

Hi cmhicks,

For my solar I had a 3m2 Kingspan Thermomax HP 200 and Themomax pump + controller fitted (like this) as I've always liked the look of Thermomax stuff. Didn't really consider using the Vaillant VR68 solar controller and the installer didn't give me the option, so that's why I have the VR65.

I'm quite pleased with the heating system so far (3 bed Victorian end terrace with better than average insulation). The weather compensation has felt to be effective so far, although I'm still not completely convinced that I have the best curve programmed into the VRC430. The 430 is not very intuitive and the manual is poorly translated from German and lacks depth. They'll nail it eventually I'm sure, but for now it's acceptable but just not super slick. I certainly don't feel like I've got a good understanding of some of the settings on the hidden setup screens. I spent about a day a few weeks ago trying to find out as much as I could about it from here and other sources online. I have a bunch of links I could PM / email you if you like. Some of them helped me along a bit.

If you have any other specific questions then let me know.

James

 

[dfaz]

The vr65 wiring center links all your controls together through the E bus system,only two wires link each item boiler, controller and vr65 your zone valves only require live neutral and earth connecting you can also use the vr10 sensor to control cylinder temperature.the advantage of this is that you can set your heating load to whatever is appropriate for your property ie 20kw but have the full 30kw on demand for hot water, you can have hot water priority or shareflow if required, it will also sense if your heating temp is rising too quickly and automatically reduce the kw output to suit, its a good bit of kit but the 430 is in my view not as user friendly as the old 400, but once set up you should not need to adjust it.

Dave.
BTW
we have just fitted one on a combi system for a customer and were advised the heat curve needed to be up at 2.7 for radiators.

 

[croydoncorgi]

Late in the day! But there are a couple of issues here.....

the advantage of this is that you can set your heating load to whatever is appropriate for your property ie 20kw but have the full 30kw on demand for hot water, you can have hot water priority or shareflow if required

- very unlikely that a domestic property would have a cylinder coil large enough to take 30kW. Having said that, it's still a very good idea to set the boiler output in DHW mode to match the capacity of the cylinder coil, whatever that turns out to be.

- the even better aspect of this setup is you CAN run the boiler in the best mode for hot water AND heating modes. Without Ebus, this is much harder, or impossible. AND, in the absence of a VRC430 controller, you CAN now make the hot water temperature control on the boiler front panel do something!

- I can't see how 'shareflow' (I assume this means heating and hot water at the same time) can be an option with a VR65 setup. If a 3-port is fitted, VR65 drives it as a true diverter valve, NOT mid-position, and with 2 zone valves, it's either, not both open together.

- the issue of whether a zone valve (potentially, an EXTRA one) is required by the Regs to isolate the cylinder from further heat in the event of an overheat situation may be trickier than implied previously. Vaillant insists that the VR10 sensor should only be fitted with a Vaillant cylinder. Technically, this is very questionable and a cynic might suggest that Vaillant just wants to sell more cylinders. OTOH, the setup has only been through certification (such as it is) with Vaillant bits end-to-end. My take on this: if you (or some jobsworth getting involved!) wants to get picky over the details, there needs to be an EXTRA method of cutting off the heat to the cylinder in the (impossible!) event of an excursion past 95 degrees. Irrespective of whether, at this temperature the boiler flue would be melting (!), the 'requirement' is for definite isolation. A method is to wire the mains supply to the whole kit-and-caboodle through the cylinder overheat cutout. That way, it will DEFINITELY not overheat. And using the existing cutout that way is MUCH cheaper and easier than fitting an extra zone valve, AND zone valves held open 24/7 DO tend to stick in the open position!

 

[dumbrill]

I've noticed that when the boiler heats the domestic hot water, the loading circuit flow temperature is a flat 80 degrees celcius. I know that the boiler is capable of modulating its burn...

A constant temperature on the flow doesn't mean that the boiler is not modulating. When the water in the tank is cold there is more heat transferred through the coil than when the water is hot. The flow temperature will be the same, but the boiler output will have modulated to adjust to the changed heat transfer. Bigger deltaT = greater heat loss.

I think the benefit you will get from adding the VR10 will be a temperature readout and the ability to change the HW temperature on the VRC430 .

 

[dumbrill]

I've noticed that when the boiler heats the domestic hot water, the loading circuit flow temperature is a flat 80 degrees celcius. I know that the boiler is capable of modulating its burn...

A constant temperature on the flow doesn't mean that the boiler is not modulating. When the water in the tank is cold there is more heat transferred through the coil than when the water is hot. The flow temperature will be the same, but the boiler output will have modulated to adjust to the changed heat transfer. Bigger deltaT = greater heat loss.

I think the benefit you will get from adding the VR10 will be a temperature readout and the ability to change the HW temperature on the VRC430 .

I hadn't read your post properly .... because you don't have a Valiant Unistor with your Valiant boiler you have to stick with the conventional overheat protection.

How the VR10 will interact with the on/off cylinder control is anyone's guess without knowing how it's all wired up.

 

[Onetap]

I've recently had the following installed...

ecoTEC Plus 624 System, VR65, VRC430 & outside temp sensor, Telford Tempest solar unvented cylinder + solar collector/controller/pump.

I've got an ecoTEC Plus 618 System, VR65, VRC430 & outside temp sensor & vented cylinder with a VR10 NTC temperature sensor. I am a G3 unvented installer.

You MUST use all the safety devices supplied with the unvented cylinder kit, i.e., you need to use the control thermostat, high-limit manual-reset safety thermostat and the spring return 2-port zone valve. You could (probably) use this in conjunction with the VR10 by setting the cylinder thermostat at 70 degC say and setting the cylinder temperature on the VRC 430 at 60 degC. The connections to the 2-port valve would then come from the VR65 and be routed to the valve via the cylinder thermostats; the cylinder thermostats should be closed at all times and would only open, breaking the circuit, if the Vaillant controls failed, the VR10 fell off or the valve stuck open. The cylinder temperature would be monitored by the VR10 and controlled by the VR65 turning the power supply on and off.

I say 'probably' above because I'm not designing this for you, the installer needs to work out the details.

My VR10 is clamped against the cylinder, under a matchbox-sized piece of insulation I cut out and then duct taped back in place over the sensor. You may need a sensor pocket on unvented cylinders with a metal outer jacket. You can't fit it on the flow pipe.

 

[Onetap]

I've noticed that when the boiler heats the domestic hot water, the loading circuit flow temperature is a flat 80 degrees celcius.

It's meant to do that, installing the VR10 won't change that.

The hot water has priority; whilst there is a DHW demand, the boiler runs at high temperature and the 2-port valve for the CH is shut. When the DHW cylinder is up to temperature, the DHW valve shuts, the CH valve opens and the boiler runs at a reduced flow temperature as required by outside sensor & weather-compensation curve set on the VRC 430.

 

[croydoncorgi]

How the VR10 will interact with the on/off cylinder control is anyone's guess without knowing how it's all wired up.

NO!!! THRICE NO!!!
The VR10 is INSTEAD of the cylinder stat, not in addition!