Underfloor Heating Mixer Valve not working

[Tim Watts]

Hi,

I just put a couple of these in:

Problem is, the mixer valve is not regulating the output reliably. eg set boiler to max (78C) and get 57C going into the UFH circuit, which is way too high - it should be regulating to 35C on MIN according to the sheet.

I'm not sure if this is a problem with my UFH circuits or that this no name valve is not upto the job. It sort of works with the boiler flow set to 55C where I run it most of the year, but I need to be sure UFH temp cannot become excessive if I turn the boiler up during the colder bits of winter.

The 2 circuits I have are:

Conservatory: about 66m JG PB 15mm pipe laid at 200mm spacing in 75mm fibre reinforced screed floating on celotex, 20m2, expected max floor output 2kW.

Shower room: about 15m pipe, 3m2, expected floor output around 300W, similar otherwise.

The seller suggested that I might want to throttle the UFH circuits with a balancing valve to try to get a 15C differential between flow and return.

I've also taken a punt on an ESBE VTA362 valve (same port layout) for £18 on ebay, really just to see if it's a drop in replacement for that one size wise and also if it works any better.

But before I go hacking around changing everything, I wanted to see if someone with experience might be able to suggest what's wrong with my setup?

Any thoughts most gratefully received

Tim

 

[ShaunCorbs]

@Uheat – Jake @Uheat – Wojtek

 

[chris watkins]

Flow rate to high I would think.
Has the pump got fixed speed settings? if so try on minimum (1).

 

[Tim Watts]

Hi Chris,

Thanks for your reply.

Yes, it's on the lowest - Level 1 Constant Pressure which IIRC is 1.5m head of water on the Grunfos curve diagram.

You think It might work better if I add a balancing valve to the UFH circuit itself and reduce the flow? That's something I can do myself as the circuit is easy to isolate from the main heating.

All the best, Tim

 

[Tim Watts]

OK - I have just received from BES (love you guys, so fast) 2 pairs of Inta rad valves - inexpensive and the check valve can take 15mm compression both sides.

As it's easy to isolate the UFH loop, I will attempt to insert these into the UFH flow just after the pump and see what throttling the circuits does. Need to be careful to leave space for a pipe stat on same pipe as a failsafe.

Think there's enough flex on the pipe to pull back to insert, but some swearing may ensue...

 

[Tim Watts]

Here goes...

Just getting the little bit of air out, boiler low, pressure topped up, valves full open (I do have 6 auto air vents on all high points so this should not take long)

Temperature meter clamped on... Let's do this:

https://i.*********/vI0EZFi.jpg?1

 

[Tim Watts]

OK - that didn't work, but it did show up something.

If I close the balancing valve right down, then open up about 1/4 to 1/2 turn which I know has some flow (did a blow test before installing), the water still goes high. I've had 60C UFH flow with the boiler producing 60-65C.

What I did notice was the top left boiler return pipe was red hot, as was the "C" side of the mixer valve. UFH return was at around 30C at this point.

The only way that could happen is if hot boiler feed water was passing directly from the H to the C through the mixer. As soon as I cranked the balancing valve a full turn open, the top left pipe + C inlet cooled due to cooler UFH return water coming in.

Boiler set down to 55C flow, UFH is getting 45C which is acceptable, but I don't think it's much down to the mixer working properly.

I have come to the conclusion the mixer valve is either faulty (I have 2, seems unlikely) or not fit for purpose (I cannot identify a maker, and I am wondering if this one was designed for under sink use only, not UFH).

After a read around some other threads, I've taken an £18 punt on an ESBE VTA362 from ebay (new) to see if it is thread and dimensionally a direct drop in for this mixer. Looks similar. At least that one is officially stated that UFH is an approved secondary use.

If it does work, it's going to be fun getting a second one as they are mostly sold in Eastern Europe (British market ESBEs have the wrong port layout with the outlet on the side).


https://i.*********/2tTqjZn.jpg

 

[Tim Watts]

Also send my findings above to the seller as a complaint and left a negative review (will be very interested if he allows it to be published).

I did wonder if I should just have made this out of parts - but I thought: "Well, this is a compact made for purpose unit - what could go wrong?"

 

[chris watkins]

Tim, the kit looks very similar to JG Speedfit single room units, looking on their spec it is only adjustable between - "Mixing valve adjustable range 47° – 62°C".
They also employ a pump controller with a sensor in the heating flow.

Have you tried using the red butterfly valve to reduce the heating flow volume right down, this may allow cooler return water temps from under floor to be available at the mixer.

 

[Tim Watts]

Hi Chris, Thanks for your reply

Mine says 35-65C with regulation to +/-2C (seller's description). Yeah - these things all look basically the same design. Mine came with an electrical thermostat inserted in the bottom of the red isolator (there's a blind port there). That is a normally open stat designed to operate the pump when there's hot flow from the boiler - many similar units do not have this. I removed this as I wasn't happy with the electrical safety (I hold a PAT qualification). As the stat appears to be there to prevent cold water circulating around the UFH loop, removing it doesn't explain the over heating.

Yes - I have tried throttling the red butterfly - in fact I have it open about 1/8 turn right now. That does limit the temperature. I don't know whether the mixer is actually regulating - I'll have to bung the boiler up to 65C and see how it reacts.

 

[Uheat – Jake]

Sorry to be a little late with the reply.

I've had a look over all the images and post explaining your issues and it appears to be the same one customers have had problems with before. Unfortunately this "No Name" mixing valve just isn't up to the standard to be used with UFH and simply doesn't do the job it's described to do.

This unit has been personally tested by a well known UFH Manufacture which is where my information regarding the valve comes from.

The only thing I can suggest is to replace the mixing unit. Like a Esbe 5kw Valve which can be found below.
5kW Underfloor Heating Control Pack / Pump / Blender

 

[Tim Watts]

Hi Uheat – Jake - thanks for that. I actually have an ESBE valve coming from ebay for £18 (VTA362 which is the plated version of the VTA352 you have)

A good result would be it's a straight swap (ports are right, so it's on the screw threads and dimensions). Otherwise it might fit with minor pipework adjustment. I think that will be the easiest solution given of the £160 I spent on the junk unit, £100 odd was for the pump and there'll be a few quid on the isolators and mounting brackets.

I could remove it and demand my money back, but it's a lot of hassle to do that (will have to drain down the main heating) and I've chucked the shipping boxes...

Wish I'd come across your site earlier.

Do you by any chance have a link to the review of the duff unit?

 

[Tim Watts]

Oh and one more thing Uheat – Jake - if the valve fits, would your company be able to sell me another (362 or 352 - just the valve)? They're rare as hen's teeth - mostly sold in Hungary, Poland and Latvia as far as I can see. I know they normally retail for nearer £100. At least I can give you a small sale in return for your very kind help here.

 

[Tim Watts]

Part arrived - 3/4" BSP. Original measures at 1" BSP. Width looks good, if I try some 3/4 to 1" adaptors. Bit short on the bottom...

 

[Uheat – Jake]

Oh and one more thing Uheat – Jake - if the valve fits, would your company be able to sell me another (362 or 352 - just the valve)? They're rare as hen's teeth - mostly sold in Hungary, Poland and Latvia as far as I can see. I know they normally retail for nearer £100. At least I can give you a small sale in return for your very kind help here.

Tim, can you send me a PM on the forum please so I can send you my email address. If you can then send me a email across with a picture of the part and the part number then I can see if we can pick one up for you from our UK Supplier.