Vaillant Boilers

[brentwoodheating]

'Under the building regs it is OK in the boiler because it still is an electrical interlock based upon temperature of the living space.'

Sorry simond- can you run that by me again.
If the stat is disabled when fitted in the facia of the boiler and all you have are TRV's everywhere, how exactly does the boiler know when to shut down-ie interlock under part L?

 

[gas4you]

Don't ask me the full technicalities, but the VRC400 has to have the heating curve set at installation. This curve relates to the room temp and the boiler flow temp and somehow this then tell the boiler when to switch off or reduce the flow temp, thus conforming with the latest regs.

I am still awaiting the revised documents that explain in simple language how this actually works.

 

[simond]

Because the VRC is a weather compensated controller, as Dave says the outside temp and internal water temp are monitored.

The correct flow temperatures are then calculated using the slope selected by the installer/user and the external weather temperature. In this way the heating is regulated by a temperature based electrical interlock and is deemed in accordance with Part L.

Correctly installed in a suitable property (with uniform insulation U values throughout) a WC system will deliver better fuel savings than a wall thermostat and a non WC high efficiency boiler. WC will allow the boiler wherever possible to run within the maximum efficiency band (eg: condense). This is why the building regs are more than satisfied.

If you choose to fit the VRC outside the boiler it can be used as a close tolerance room stat and tweak the WC curve, but on a properly set up system this is not necessary.

 

[brentwoodheating]

I understand the principles of weather compensation controlling flow temp but would expect to fit the unit (not the outdoor bit!) in the same position as a room stat so the boiler would switch off when satisfied.
I don't see how it can comply with Part L if mounted on the boiler with no ACTUAL reading of the inside temp? It appears that mounted on the boiler it just sends out the flow temp that would achieve the differential between outside and inside- but has no way of knowing if or when its gets there. So putting the whole house was on TRV's appears to be a crock because it would just keep on cycling because it only knows the temp outside not both.
Will have to ask Vaillant because that doesn't sound right.

 

[UF6]

As the rooms heat up, the return temperature will rise and this will switch off the boiler.
I'm not sure if the Vaillants look at the return temp independently or the reduction in difference between flow and return temp.
With variable temp., you don't need a room sensor/stat to switch off the boiler.

 

[Agile]

Gas4U

Surely Dave, whatever cylinder he is using th VR10 NTC will give better control than an on/off cylinder stat?

If its just the dry pocket aspect then that is easy to overcome by fitting it so its pressed up against the copper tank with heat transfer paste.

Tony

 

[simond]

A weather comp system tends to run at much lower temps for most of the year.

Some WC systems (eg: Viessmann) keep the circulation pump running even during boiler off periods to distribute the heat across the property from warmer rooms to cooler ones, all the time the outside temp is cooler than the inside temp.

Therefore the room stat is not a critical energy saving measure, it is just a fine setting.

You will find that a VRC400 does meet Part L when mounted in a boiler. We have been fitting them for a few years now, and their Viessmann counterparts. You have a lot to learn, grasshopper .

 

[gas4you]

Tony; Take your point and I suppose you are correct.

Brentwood; You set the required room temperature on the VRC400 when it is on the boiler front.

Because of the heating curves set this will turn the boiler on and off like a traditional stat but including allowances for the outside temp.

As I say I am awaiting a re-written manual by one of the Vaillant tech managers who is writing it in laymans terms.

I doubt very much if the normal tech support staff will know either, especially if you call on the usual tech number as these will probably be Glow Worm numpties in front of a PC

 

[brentwoodheating]

So, according to the outside temp, the curve set according to the U value of the building, and the desired temp set on the 400, the flow goes out at X and when it comes back at Y the boiler shuts off. Got that bit master!
How does it know to turn back on again- or is that the pump keep running bit so that the return is measured? Or maybe the pump fires periodically to check?
So TRV's all round works because when they re-open the flow temp drops and away the boiler goes. A little like that Potteron that's on a flow switch.
If that's it then I get it. Questions answered- thankyou.

 

[Agile]

Because of the heating curves set this will turn the boiler on and off like a traditional stat but including allowances for the outside temp.

I think that the boiler will actually control the flow temperature to that value which it has calculated by reference to the outside temperature is required to provide the required internal temperature.

The boiler will modulate back and if thats still too much power will stay off for a minimum of its anticycling delay or longer if the flow temperature is still within its set hysteresis level.

Tony

 

[eyeofthebeholder]

Hi Guys,

Sorry to pull up an old thread, but I'll still continuing to look at which control panel I want.

Just noticed on the Vaillent website that they have released a new controller/timer - the VRC430.

Just wondered what are differences with the VRC400 - apart from the obvious blue backlight as it says in thr title it is 'programmable'.

Cheers

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