We have a problem…

We had a nice Vaillant unvented system fitted 2 years ago.

System boiler & 430 control, unvented cylinder, weather compensator thing. All the rads on TRVs, no room thermastat and although I couldn’t get my head round it, it’s worked a treat and has been brilliant. Each room is totally controllable via the TRVs.

Now we’ve had an extension done and added 40sqm of wet (Polypipe) UFH. This is split into 3 zones each with a stat.

Our HE can’t get the current system to work with the UHF, own pump, own stats etc.

So the weather compensator is being ripped out, we’ve got an old style thermostat on the wall and it’s just not as good. Parts of the house cold etc not ballanced how it used to be.

He’s spent hours on the phone to Vaillant but says it can’t be done we have to lose the all the good stuff and take a step backwards? 🙁

Any ideas?

run the UFH on it’s own pump and room stat (honeywell CM927 is a fave in here). Leave the vaillant to look after the tank temp on it’s own.

The UHF has three stats and one pump

then shirley it can just draw from the cylinder and the valliant controls will top up the cylinder temp as and when it needs to? The funky weather compensator stuff shouldnt come into it.

Is your ufh zoned? presuming you have two zone valves, one for heating one for hot water, a third should be fitted for the ufh with means of control eg seperate timeclock/programmable t/stat or replace existing with 3 channel programmer. its no use having rads and ufh both coming on at the same time as they heat up at different rates. ufh wants to be on a couple of hours before the rads to heat up the slab(presuming ufh is in a slab?). i would have left your system as it was and added a programmer to control the ufh and boiler by itself.
i have no idea why vaillant would say that imo its perfectly fine, even if your boiler was undersized now because you have added more space to your home, if it is done how i would do it you will not really be heating the whole system at the same time.

stoner, im presuming he has a megaflow style cylinder and not a buffer tank as you are thinking?

Waiting for the outcome of this posting.

I looked at UFH heating for my extension but ruled it out. One reason, there were a few, was integrating the system into the current arrangement similar to yours, i.e unvented tank, indirect, with boiler.

The engineer’s concern was flow and balancing the system not helped by the mircobore arrangement. From what I recall a flow restricted was required to promote flow through the UFH and that I needed to go back to the mircobore manifold. I switched after that point……

programmer to control the ufh and boiler by itself.

without a buffer, then as you say, it just needs a boiler control to work with the UFH stat demand.

pjm84 your engineer has been honest balancing/ flow is a mare. The issue isnt with your boiler its the way its being used supreme bean has the correct idea seperate zone valve and controls.. you ll in enevitably be frustrated i’m afraid as ufh will as stated need to come on much earlier and come off quicker too as heat is retained for longer
this is one of the issues that new owners of UFH and wood burners regulary question.. why cant i turn it down/ why doesnt it cool down quicker/ why do i have to wait so long before the room is warm..

one customer even had us install a seperate boiler just for her bedroom and ensuite ufh and hw…

Ecotec system boiler & Unistor cylinder (Hot water & Rads) Unvented so runs at main pressure.

3 zones on the UHF (Kitchen / Kitchen 2 / Wet room)

Tiger6791

Where are you based?

One of my best mates is a service engineer for them, I’ll point him the direction of this thread and see what he suggests you should do…

I installed some designer radiators and junked the UFH. Not sure the OP wants to hear that though.

Yep off course another of the issues was the slow reactive times (thermal mass).

Supremebean is right. You need to run 3 zones off the main boiler flow. CH (rads), CH (Underfloor) and HW.

I would ask your engineer if he has taken a feed for the ufh off the boiler flow BEFORE the ch and hw motorized valves and fitted a new motorized valve to control it. as i said above is the only way it will work satisfactorily. if it is connected after the heating valve its not going to heat up too well.

Can’t see any reason why you can’t get all of that to work together, speak to a guy who understands system design.

There is also a couple of products around that may get round your problem (triple coil cylinder that uses one coil as a supply for underfloor in a thermal store type of way)

And the problem isn’t Vailant but someone not understanding how to intergrate the systems.