Ebus and boiler modulation

[ah101]

Hi,
I recently have had a new vaillant boiler ecotec plus 415 installed. It's a conventional system with single zone heating and a hot water storage tank. This is the first boiler I've owned with modulation capability. At the moment the room thermostat is a simple on or off type. The boiler does do some form of modulation using flow and return water temperature. I am wondering if it would make sense to install a VRT50/2 ebus thermostat? If I do install that, would that automatically override the flow and return modulation? I'm fairly handy but the last boiler I had was 30 yrs old so I did get my money's worth out of it but I'm now way behind in tech knowledge on modern boilers!
Thanks for any help with this.

 

[muggles]

It's not quite that simple, you'll need to replace your existing wiring centre with a VR66/2, and of course make sure you have the requisite cables to actually complete the job

 

[ah101]

So I can't simply disconnect my existing thermostat, run a new cable from the ebus terminals at the boiler direct to the ebus thermostat.

 

[Harry Bloomfield]

The boiler does do some form of modulation using flow and return water temperature. I am wondering if it would make sense to install a VRT50/2 ebus thermostat? If I do install that, would that automatically override the flow and return modulation?

Yes, but as above, you will need at least VR66/2 to go with it, and possibly the timer too. Rather than the boiler modulating, based entirely on flow and return - it will modulate based on actual room temperature and demand. It will put an end to the boiler running flat out, until it decides it needs to modulate - instead it will modulate from the beginning, knowing how much heat might be needed. Pipes will no longer creak and groan, as the boiler fires, then pipes cool, you just get a steady, better controlled temperature in rooms, and from the radiators.

 

[Harry Bloomfield]

So I can't simply disconnect my existing thermostat, run a new cable from the ebus terminals at the boiler direct to the ebus thermostat.

No, you need as a minimum, both parts. You also need boiler, VR66 and boiler, linked by a pair of wires for the ebus.

 

[ah101]

Please excuse my ignorance in all this!
At the moment the system has a timer for the hot water and the central heating which I'm happy with. The hot water is heated for 1.5 hrs in the morning and the central heating for 1 hour in the morning and 6 hrs in the evening. What I want from the thermostat to do is just modulate the central heating when the timer switches it on and obviously the thermostat is calling for heat. So from what I understand just installing the ebus thermostat would get the boiler to modulate when the timer has turned it on and the ebus thermostat is calling for heat.
Sorry for being a bit dim about all this!

 

[ah101]

thermostat WOULDN'T get the boiler to modulate

Correcting a typo error from before.

 

[Harry Bloomfield]

thermostat WOULDN'T get the boiler to modulate

Correcting a typo error from before.

Reading the VRT spec. it suggests it will work with the boiler, to have it modulate the boilers output.

VRT 50/2 | Digital Room Thermostat | Vaillant UK

The sensoROOM pure Digital Room Thermostat is easy to use and shows the current room temperature. It can also be set to intelligent control which provides greater efficiency and a more comfortable room temperature. Find out more.

professional.vaillant.co.uk

'Enhanced load compensation - uses enhanced load compensation to adjust the output of the Vaillant boiler, ensuring it only uses the energy needed'

In other words, unlike a normal thermostat, which simply switches the boiler on and off, the VRT tells the boiler, via the ebus, precisely how much heat it needs to generate, to match the need for heat. In other words it controls the boilers modulation directly. That's how I read it, anyway, why else would it need to use ebus, if it only switches the boiler on and off?...

There are better Vaillant control systems than this. Mine, which is now an obsolete - certainly takes control of the modulation, and is wireless, a VR470F. It includes timer, 'thermostat', and remote control, in the one, portable unit. I bought the full package 470F control, the equivalent of the VR66, which goes in the airing cupboard, wireless receiver to go in the boiler, VR10, which senses and reports back the actual temperature of the hot water cylinder, plus the outdoor wireless sensor, so the system can take account of that too, when making it's decision on how much heat the boiler needs to produce.

 

[muggles]

Yeah don't try to mix eBUS and 230v wires, that will go very very badly for you. You need to daisy-chain an eBUS cable from the boiler to the VR66/2, and on to the VRT50/2

 

[Why Not Indeed]

The boiler will modulate without some fancy external controls, but it will perhaps start out higher than strictly necessary. I am not sure how noticeable it would be if my boiler had just stayed around 25% modulation all day:

 

[Harry Bloomfield]

The boiler will modulate without some fancy external controls, but it will perhaps start out higher than strictly necessary.

and continually cycle on and off, on a normal on/off stat.

 

[ah101]

Thanks for all the replies.
So looking at the info I have now got. Appreciating that although the vrt50/2 is maybe not the best ebus control, it will modulate the boiler better than flow and return water temperature and with the vrt50/2 connected it will override the flow and return water temperature way of modulation.
Sorry to keep banging on, I just need to make sure. The on/off thermostat I've got fitted is a very good one with a 0.4°C hysteresis and I don't want to invest in something that will give me less control.
Thanks.

 

[Why Not Indeed]

and continually cycle on and off, on a normal on/off stat.

It depends. Mine didn't. It was firing for the whole 7h in that time window. But I am cheating by having the flow temperature set low enough that the thermostat is never satisfied.

 

[Harry Bloomfield]

It depends. Mine didn't. It was firing for the whole 7h in that time window. But I am cheating by having the flow temperature set low enough that the thermostat is never satisfied.

OK, that will work, but only providing you manually set and adjust the flow temperature.

 

[Harry Bloomfield]

So looking at the info I have now got. Appreciating that although the vrt50/2 is maybe not the best ebus control, it will modulate the boiler better than flow and return water temperature and with the vrt50/2 connected it will override the flow and return water temperature way of modulation.

Yes, but you could maybe ring Vaillant and confirm that is the case, before committing to buy.

Sorry to keep banging on, I just need to make sure. The on/off thermostat I've got fitted is a very good one with a 0.4°C hysteresis and I don't want to invest in something that will give me less control.

The smaller the value of hysteresis, on a conventional on/off stat, the more frequently your boiler will go through a wasteful start up, and shutdown. Something which an ebus connected control can for the most part avoid. On ebus, when it sees a demand for heat, it will start up on full power, for a few seconds, to establish the flame, then (knowing exactly how much heat is needed) immediately modulate the boiler to match that demand for heat. That way, you get a longer slower, more efficient 'burn', more value out of the gas burned.