Modulating control for a valiant boiler

I’ve just fired up the heating and remembered how annoying it is.  I have dual zone (rads & ufh) using 2 different on-off controllers. Both of these do time proportional integral (switch heating on and off 6 times an hour) and cause the boiler to go into anti cycle mode until the house cools down enough for them to ask for heat continuously. Then the boiler senses the return temp is too high and shuts off.  It sort of works but its crap.

I want to be able to control dual zone heating with zone valves and have the boiler modulate it’s output based on demand from both zones – not just on\off.

I can fit an opentherm adaptor but not supported in the UK (EU only), or valiant solution although I’m not sure they do what I want, or something else?

I did a huge amount of research into this before having my new boiler installed at the end of the summer. My plumber and I went through all the third party offerings from Hive, Nest etc as well as looking at what boiler manufacturers offered.

The short answer is buy a Vaillant control. They’re the only ones that can properly modulate a Vaillant boiler using eBus. All the third party ones just switch it on and off a lot which means it can’t hit its condensing point well or modulate down.

I have an ecoTEC 627 Exclusive system boiler, the SensoComfort VRC720 controller and the SensoNET VR921 internet gateway so I can nerd-out and fiddle with it from my phone. I picked that controller because it can run up to five zones and Vaillant’s connected TRVs and give room-by-room control. The SensoHOME controller will also run a couple of zones, but not the TRVs.

https://www.vaillant.co.uk/for-installers/products/latest-innovation/senso-range/#:~:text=Control%20options&text=sensoHOME%20is%20a%20single%20heating,up%20to%203%20heating%20circuits.

What Ben said.

Just had the same controls fitted with our new Vaillant boiler, along with en external temperature sensor for weather compensation. We previously had a Nest in our old place. While the Nest was a slicker interface, the level of control the Vaillant controller gives is huge, plus of course the modulation.

Thanks, sounds like the controls have moved on since I last looked at it.

Just had the same controls fitted with our new Vaillant boiler, along with en external temperature sensor for weather compensation

+1 on this.  You absolutely should be using weather compensation as the primary driver of your heating, especially if you’ve got wet underfloor heating.  Useless British heating engineers set everything up with stupidly high flow temperatures which mean your room temperatures overshoot, and the return temperatures to the boiler are high which means the boiler operates inefficiently because it’s not in condensing mode.

Basically – if you can see a plume coming out of your flue pipe it is not condensing (ie it’s not operating at full efficiency).

It’s far more efficient to run your rads (and especially your underfloor heating) at lower temperatures with a longer on period.  Weather compensation varies the flow temperature based on the outdoor temp.

My house is very well insulated with UFH throughout.  Flow temperature is only 27C at an external temp of 0C.  At 10C external flow temp is just 23C. I don’t actually have any internal thermostats at all – i had a few thermometers while I was tweaking the heating curve but now it’s right it just works. The only time it’s NOT in condensing mode is when it’s heating water.

Looking at it right now it’s 11C outside, the flow temp is 22C and the boilers modulated down to 14%.

It doesn’t even need turning off in summer – it’s ‘off’ if the external temp is 13C or higher, when it drops below that it starts running

https://www.vaillant.co.uk/global-search/?q=Weather+Compensating+Thermostats

According to this most UK gas boilers in reality are 10-20% less efficient than they could be since
– they are oversized
– set to high flow temps
– use simple on-off controls rather than weather compensation (which varies flow temp) and modulation (which reduces boiler power)

Usually only the boiler manufacturers own controls allow weather compensation and modulation.

https://www.theheatinghub.co.uk/are-we-being-mislead-over-boiler-efficiencies-erp-sedbuk