UFH mixing valve not restricting heat to floor

[Dtwone]

Hi, I've installed a 2 zone kit that uses an RWC mixing valve, Thermomix with hot in, return to boiler and heat out to Ufh pump and return from floor manifold. From underfloor heating store but basically the same as a jug speedfit Ufh kit.
I thought I had a duff thermostat inside the reliance mixing valve but they supplied me a service kit and it's still not working.
The thermostat expands and contracts as it should, I tested it in a bowl of warm water, allowing the hot feed from the boiler to bypass the Ufh manifold but the inlet temp on the manifold is rising to basically as high as the boiler feed in, abou 65 degrees and the mixing valve control has no effect on any setting, I have just converted a y plan system to s plan with a separate zone for the Ufh and the return goes back close to the boiler return into the boiler. I've also fitted a bypass valve which you can hear opening when the boiler pump is on overrun and all zones have stopped calling for heat.
I'm really stumped, it's like the main system pump is overwhelming the mixing valve but it's running quietly on minimum setting.
I've no issues with the hot water or radiator zones or the boiler, and the Ufh manifold appears to be working fine and both loops heat ok, it's just there's no control of the temperature down to the 45 degrees needed for the floor.
I even tried restricting the flow to the valve by partially closing a full bore 22mm isolation valve I fitted in the supply to the Ufh zone but you have to almost shut it off completely to make any difference. There's no other parts in the mixing valve other than the spring and wax stat so nothing else I can see is wrong, I've tried the Ufh pump on different speeds, Ufh zones open or restricted, nothing makes any difference.
Any help would be great as I can't see anything wrong with the layout and components I have and I'm pulling my hair out with 50 degree water coming BACK OUT of the floor after nearly 50m of pipe run at the moment!!!

 

[ShaunCorbs]

it's a bit deceptive but it's within the Gas Safe general requirements and also the manufacturer specific requirements for distance from wall, below opening window and from roof line and roof windows, this was installed by a gas safe engineer too.

What boiler is it ?

 

[Dtwone]

potterton suprima 60 non condensing

 

[ShaunCorbs]

So it's a min of 1m away from the window/wall?

 

[Dtwone]

So it's a min of 1m away from the window/wall?

yeah, 3 maybe 4 roof tile lengths and its a very low pitch 12.5 degree roof so not much length of tile lost in the incline, fitter was not initially sure so actually called Gas Safe to get his interpretation of the diagrams confirmed, it's close to max length of that flue allowed on that boiler with the elbows included but it actually ran better emissions when tested than the original short straight flue did - go figure that?

 

[ShaunCorbs]

I would say it's too close

 

[Dtwone]

I would say it's too close

I'm not questionning the the requirements but it's actually further away from opening windows (both horizontally and vertically) than the old horizontal flue was when the house was newly built, silly house layout with the flue going out of the back wall rather than a side alley.

 

[Dtwone]

well, as a follow up to my call today RWC technical have replied via email and OK'd my install from my description and photos, their advice is to try restricting the zone actuators and then get a new valve body so hopefully I'll get to the bottom of this soon.
Thanks again for all your suggestions, I'll let you know the outcome.

 

[Ric2013]

Thanks again for all your suggestions, I'll let you know the outcome.

I for one will be interested to hear back from you.

 

[Dtwone]

I for one will be interested to hear back from you.

Well its not an over specced pump, with both actuators almost shut off it shot up from 17 degrees to 65 on the manifold input within 10 minutes new mixing valve it is then, you never know perhaps I dropped an olive into it?

 

[Dtwone]

Well I think I've sussed it, I removed the valve to watch the stat react to hot water from the side connection, the stat didn't move at all so I removed the control tap and then the stat and Spring, I then reassembled with no spring and repeated. Still no movement of the stat, and then I realised the stat didn't recess further than flush with the tap base which means no return flow can mix into the inlet through the stat to the pump.
Basically the drilling in the valve body the stat recesses into isn't machined far enough to allow the stat to open!
This also explains why when I wound the tap into the minimum position, if not when it was factory assembled, the stat pin was crushed into the wax body so it appeared damaged when I compared it to a new one.
Pictures uploaded show how the stat plastic surround is flush with the brass body of the tap face when the tap is screwed in, I'll mail the info and pics to RWC but I'm pretty sure it's a manufacturing defect, typical when this is the first time I've used or seen one.

 

[Ric2013]

I've never had to take one apart, so can't comment, but I like your investigative approach... let's hope you're right.

 

[Dtwone]

Well it's sorted, just before Christmas I bought a new RWC mixing valve.
So it was the valve that was faulty but not in the way I had thought.
Turns out the brass tap mechanism that was fitted to the original unit is incompatible with the main casting and thermostat!
Basically the new tap has a different rear face that essentially makes it shallower and allows the water to flow and the stat to open. I couldn't resist so took the new one apart to investigate!
In the images attached you can see the new assembled unit at room temp with the stat very slightly open from the tap face, i.e. allowing a small flow of returned cooled water from under the floor. The old unit is jammed shut at any temp.
In fact as I'd discovered before, the old unit doesn't allow the stat to move at all, and worse than that as the tap face extends as you dial the temp down it crushes the stat pin into the wax and damages the stat!
The interesting thing is that I've carefully measured all of the new casting and it is identical to the old one so it's only the new tap that is different.
In the new year I'll ask RWC what is going on, because I'm interested to know what has happened here as the valves have the same part no??
The retailer was pretty poor, basically they only supply a whole kit with this valve and pump, so I'd have to pay packaging to return, £250 for a new valve and inferior pump or over 500 for a new kit and then wait weeks for a warranty claim. In the end (and actually suggested by the retailer - cheek) I bought a new valve for £100 from a different supplier to get it in a couple of days and took the cost myself. Bit annoyed and won't be recommending them to anyone soon.
Bottom line is there was nothing wrong with my self-install, it was a really odd, hard to diagnose fault with the mixing valve so I thought I'd share the detail.
I now have a steady 45 degree flow and a very happy cat lying on the new floor

New unit slightly open to return flow at room temp:

New tap has the protruding ring, but shallower main base surround

At initial low temp the input thermometer reads what I'd expect now, at about 42 on the knob it runs at a steady 45 regardless of other demand on the boiler

 

[Ric2013]

So, it was equipment failure after all, not an installation error. Good good, glad you got it sorted. Unfortunately most things seem to be built and sold with low margins and this is the sort of sheight that we end up with.

As an aside, I know a plumber who insists the reason a TRV he installed won't allow any hot water through on any setting is that the customer puts her open-shelved TV stand in front of it, thus restricting airflow. I've seen it, I think it's a faulty TRV, as I don't think the shelf can possibly restrict airflow by any meaningful measure, but he was trying to train me so I just nodded politely. The lesson I learnt was to always blow through TRVs I'm about to install and check they are all roughly in calibration with one another, then they should all work about the same as one another. But on the production line, this would cost a few extra pence, which means that by the time it gets to the user, that's another £5 or so. So, sadly...

Going back to UFH, I used a different supplier and was very pleased with the quality of some of the components, and thought others were pants. Only reason I bought the kit was that it was easier to argue potential problems if I had used a kit, rather than make it up myself. I did suggest improvements to the firm, giving them some potentially valuable(?) feedback on what I liked and disliked (it was about 50/50), but they didn't seem that interested (I certainly never heard back) or even that knowledgeable about their products.

 

[JonnyF]

Hi. Only just skimmed the thread but this seems exactly the same issue I’m having with a Polypipe 4 port set up and pretty poor technical support from them. Would there be any chance I could speak to you on the phone please rather than send messages back and forth? Thank you