Underfloor Heating - Sticky John Guest Speedfit Mixer?

[starboy]

Hi

My first post so hello to you all and I hope i'm posting in the right place.

Having an issue with my underfloor heating. When it is switched on via a Hive interface, boiler (in garage) switches on and temp on its display drops but steadily rises. In the photo after a recent switch on it shows at being at around 59C. Below it is a DAB Evosta 3 which i believe is in constant pressure with the highest flow setting (3). Following the pipework down from this the copper pipe before and after the silver box marked "UFH" runs hot.

And indeed at the manifold which is under the stairs, the supply from the water runs hot. But here seems to be a problem. The Speedfit Underfloor Thermostatic Mixing Valve (set at 40C) doesnt seem to be allowing water through into the manifold and subsequently in to the floor. The lower return manifold instead gets hot.

It is only when i turn the Speedfit valve down to 35 or lower that water flows through the top manifold and the red flow meters show flow. What is strange is that i can turn the temp back up to 40C and the water still flows. I would say this happens the majority of the time, and initially i thought the water from the boiler wasn't hot enough for the valve to allow it through into the floor but i dont think this is the issue.

Furthermore on the Grundfos UPM3 Auto i'm pretty sure i have it configures correctly for underfloor heating (constant pressure, green light, blank light, three yellow) with again the highest flow setting although the flow shows just two yellow LEDs most of the time. So is it just a sticky Speedfit valve or something else? (A month or so back the Grundfos UPM3 Auto had got stuck (red light and clicking noise) and me and my dad took it apart and freed it)

I have attached as many photos as i think might be useful (including settings)

Thanks in advance for any help/advice.

 

[MeldrewsMate]

Is the Grundfos pump pumping in the correct direction? Upwards? You said you'd had that apart to unseize it.
Did you take out the whole pump body or just take the four allen headed screws out and split the body from the motor? The bulbous part of the body should be lower-most. Easy to see once you know it's not symmetrical.
Turning the temperature setting low will cause all the flow to recirculate, effectively cutting off the primary flow from the boiler.
Does the boiler flow (hot pipe) come in from the bottom of the temperature setting valve?
Did you remove the DAB pump also? Could that be upside down - in your installation it should pump away from the boiler (pump downwards)

 

[starboy]

I'm pretty sure it is in the correct direction. i've attached a photo of the sideview and you can see the bulbous part is at the bottom. When it was taken apart the four allen head screws were removed and body split from motor.

I'm not sure if the hot pipe into the bottom is from the boiler. it is definitely hot when system is switched on but so is the one coming out the right-handside of the speedfit valve.

after the speedfit valve is turn back and forth a few times., the water flow does also start and the floor warm up with top manifold getting warmer and the lower one too (although slightly cooler), so i would assume everything is installed in the correct direction.

The DAB valve wasn't removed but we get hot water and radiators working fine with flow coming through that same pump, so again i think it is in correct direction?