Are Vaillant controls worth the investment?

[windsor-tg]

I am considering replacing my existing boiler with the new 2023 Vaillant ecotec plus 625 boiler. I currently have 3 x Heatmiser neoStat thermostats that are all hard wired back to the wiring centre; one for the central heating, one for a room with UFH, and one for the HW. I use the Heatmiser smart app on my phone to control the heating.

I have read conflicting opinions about Vaillant controls; some people recommend the Vaillant controls as they modulate the boiler better, maintain even temperature within the house, and this makes the boiler more efficient. Others, however, have said it is a large investment that will take several years to get your money back.

I have had a look at what Vaillant controls I would potentially need, and the cost is in the region of £800

Is it worth investing ~£800 for Vaillant controls or just stick with my Heatmiser setup?

 

[Chuck]

It's tricky to measure the savings, if any, that sophisticated controls make. This observation alone is enough to tell us that the savings are unlikely to be more than a few percent.

The Heat Miser thermostats you have use on-off control with an adjustable hysteresis band. Changing to a type that uses TPI control, which typically allows tighter control of the room-temperature, might allow you to reduce the average temperature by up to 1°C while maintaining the same level of 'comfort' (or discomfort!) for the occupants. That could reduce the CH element of the gas bill by up to 10% (if you're lucky).

So, for example, if my gas bill were £2000 a year I'd expect the Vaillant Controls to save £100 a year so that's 8-years to break even, which I don't find very compelling but others might.

To be honest, once you have your boiler controlled by a programmer-thermostat, or something comparable, you need to look elsewhere for significant savings in energy: better insulation, turn the setpoint temperatures down, wear warmer clothes. It's disappointing, but that's physics for you.

 

[elitegascare]

Depends on how the boiler is installed. If on S or Y plan, the boiler is fixed at a set output temp for heating the cylinder and and CH. So is pretty much on or off from what I can tell.

If you need to spend £800 on controls on top of the boiler cost, I would be looking at a boiler that will control all the correct things out the box - examples are Alpha, Atag, Intergas. For good efficiency you need a boiler setup to do weather compensation, you can then set a curve that gives lower output temperature based on outside temperature. If you have radiators where the controller sits, load compensation is also good.

None of this will fix your short cycling on UFH when that is run in isolation, without some form of buffer or volumiser.

 

[Last Plumber]

They work very well in my experience. If you,re going for a new Vaillant then yes, I would go for the weather compensating controls for it. Sensocomfort is the way forward. I would avoid the Vsmart.

You should be able to set water and heating separate form each other. The weather compensating feature on sensocomfort works well so long as the installer is used to configuring it.

I installed it in my own house to test it thoroughly prior to recommending it to customers.

 

[John.g]

Assume a 25kw boiler with a minimum output of 6.5kw.
UFH brings its own challenges even if its demand is allways greater than the boiler minimum output.
For example assuming the UFH TMV requires a dT of 10C to operate properly then a UFH demand of 7kw with flow/return temps of 45C/35C will require a flowrate of 10.04LPM with 5.02LPM recirculating through the TMV and 5.02LPM returning/flowing through the boiler at a dT of 20C.
The problem arises when the boiler fires up, most gas boilers fire up at ~ 65% of their rated output so a 25kw output boiler will fire at 16.25kw and require a flowrate of 9.32LPM to prevent the dT rising above 25C for the ignition period which then requires a very short ignition time as the boiler HEX "buffer" of say 3L will only supply enough cool water for around 20secs or so, this why a volumiser may be required if the ignition period is longer, Vaillant may now have got this right down with the newer models but there are numerous posts/complaints of Vaillant ignition periods of 60sec.