UFH mixing valve not restricting heat to floor

[Dtwone]

Yes, you're right there is an embossed arrow on the side of the new pump and it is going up the flow is right and the flow valves seem to adjust the two independent floor loops fine, one run is about 3 times the other.
It takes a while to get all of the air out of the main boiler circuit when I've drained out the mixing valve to change the stat but I know I bled the Ufh loops well and the air bleeds on the manifold work fine and the Ufh pump runs quiet and smoothly, there's a manual air bleed in the airing cupboard just after the HW tank 2 port, that traps a little air but the main trap is a taller bathroom towel radiator which was originally just a standard lower rad, changed by the previous owner. I've put an Saladin auto vent on that but it seems to stick too easily even though the system is very clean.
The original setup was a conventional y plan with a tank side flange for the showers and an always on T for the bathroom rads. the boiler is an old but surprisingly capable potterton suprima 60 that has no trouble meeting demand and its own temp dial is only ever needed at about 1/3. The main system pump is on minimum setting a is the Ufh pump.
I removed the y plan 3 port and changed to s plan 2 x 2 ports first, then when I was sure that all worked I joined up the Ufh as a Third zone. It looks a tangle in the airing cupboard but it's pretty straightforward just a small space with a few more elbows than would look nice and neat.

 

[Dtwone]

I haven't read the whole thread in detail, but it seems to me that the water is being circulated through the UFH emitters too fast. This means it doesn't have time to cool enough to be able to reduce the the incoming flow to the correct temperature in the mixing valve. This will give a runaway effect where for the first few minutes the water going to the UFH emitters is the right temperature but it then ramps up until the mixer is ineffective at cooling the incoming flow.

If I'm right, the remedy is to reduce the circulation by turning down the pump and/or the balancing valves on the UFH emitters.

Whoever designed the system should have calculated the circulation rate and matched it to the amount of power that the UFH needs to emit.

It's an underfloor heating store 20m2 kit with matched components, I've only used about 3/4 of the 100 m of barrier pipe but the 2nd smaller loop is restricted to about 1/3 the flow of the larger one. I have the Ufh pump running on the lowest setting.
When the system first runs, say first 30 minutes or maybe more from totally cold it still doesn't cool the incoming flow, the return gauge may be under 20 degrees but the input can rise to over 60 still.
I'm sure I've run it with the emitters set low but I'll try it again with both of them set to near minimum.

 

[Chuck]

When the system first runs, say first 30 minutes or maybe more from totally cold it still doesn't cool the incoming flow, the return gauge may be under 20 degrees but the input can rise to over 60 still.
I'm sure I've run it with the emitters set low but I'll try it again with both of them set to near minimum.

Okay. If the mixing valve has equal amounts of 60° and 20°C water available it should certainly be able to regulate its outflow to ca 40°C.

Assuming you have got the flow and return connections to the valve round the right way and have replaced the cartridge perhaps there is a manufacturing defect in in the cast body of the thermostat causing it not to shut off in the incoming hot.

Ask the manufacturers to let you have a replacement to try.

 

[Sharp Point]

Okay. If the mixing valve has equal amounts of 60° and 20°C water available it should certainly be able to regulate its outflow to ca 40°C.

Assuming you have got the flow and return connections to the valve round the right way and have replaced the cartridge perhaps there is a manufacturing defect in in the cast body of the thermostat causing it not to shut off in the incoming hot.

Ask the manufacturers to let you have a replacement to try.

I agree, the finger points to this if all the pipework has been installed correctly.

 

[Dtwone]

Thank you for your replies, I spoke to UFH store last week and they want me to buy a new one and then get a refund if they deem the old one to be faulty - not overly impressed at over £100. I did get through to RWC technical dept who were very helpful and sent me a service kit free of charge as I was sure the original stat was duff, but thinking about it now I may just have crushed the stat pin into the body too far in my enthusiam to get it to operate at a lower temp, this is easy to do if you remove the plastic collar on the control knob and keep turning
I will try RWC again but I've checked everything else over so many times, I'm sure of all my connections and the system is flowing to and from boiler and heating the manifold/floor fine it's just there's no feedback control of the UFH circuit as the water temp flowing over the stat rises.
I eventually just about figured out how the 4 port mixing valve casting works, it's not immediately obvious but it has side channels as well as the main stat/control casting.
This 'Thermomix' valve is quite widely used and the same part manufactured by RWC is used by JG Speedfit so it's not like it's some dubious import or something. I'll call RWC again and let you know what they think.

 

[oz-plumber]

Gee Pal,

You're a hard nut to please!

You've done all the work yourself, altered the configuration of your heating system, added UFH and then you have a problem and you blame it on the equipment.

You have had a thermostatic repair kit supplied free of charge and then you admit to probably stuffing up the first one and now the second one.

You have had the supplier of the heating equipment offer you a full refund on the mixing assembly if the one you have is faulty.

What do you expect?
A complete replacement without them checking if the unit you installed is faulty?

As far as I can tell you are getting as good a treatment, if not better treatment, than some of us in the trade get.

I would say that you are now in the position to pay someone who has experience in heating systems to check the system over.

There's obviously a problem somewhere, but after replacing 2 thermostatic sensors and now wanting to replace the mixing block, it would seem less likely that there is equipment failure

 

[Dtwone]

yep, I may seem hard to please and I understand the suppliers position but I'm also quite technically minded and not overly impressed by their attitude in providing any level of technical support, they basically told me they never have problems with their mixing valves and to contact the manufacturer, they don't seem to know their own products very well - Unlike the RWC tech guy who was very helpful and confirmed my understanding of the operation of the valve and stat. It's hardly demanding to expect some level of customer support beyond a list of parts supplied.
I think I've explained and covered everything in my system to you guys on here and thanks for the responses, it's confirmed my thoughts and reassured me I've not overlooked something fairly obvious.
If you'd like to see the fruits of the rest of my efforts, pics attached. This is my biggest project yet and has taken me 18 months of evenings and weekends but I'm very pleased with the result and so are building control.

 

[ShaunCorbs]

One major problem and I would be worried about is that flue is very dangerous and needs turning off

 

[Dtwone]

been onto RWC again, like one of you suggested they also think restricting the flow controllers right down is worth a try.
Maybe the Grundfoss pump in the kit is just too powerful (even on low setting) for a smaller setup? It is used on the manifolds with many more loops but he thinks it's possible it's just overwhelming the return from the floor with the flow rate I've had it set at.
He's also asked for pics of my whole system to take a look over which was very good of him, now that's what I call good service and a company I'd recommend to anyone.

 

[Dtwone]

One major problem and I would be worried about is that flue is very dangerous and needs turning off

it's a bit deceptive in the picture 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.