Mixing Pressure Problems

I have a rather large wet UFH system. Water is flowing around the system, but I don't get any (or minimal) hot water injecting from the primary boiler flow into the ufh system. this means the mix temp never gets above 20 degrees.

I think that the ufh system's pressure might be too high which is causing it to backflow into the t junction where the mix occurs and then this water gets backfilled into the system, backing up the hot water from the boiler.

I've tried fiddling with the diverter valve, but it's so fiddly that half a degree and primary loop goes from cold after the divert flow to red hot!

Pic below if it helps.

I think that I need to reduce the pressure of UFH system but other than that, no idea.

Will try and assist.
I have only seen one UFH system but assume they are all similar, ie the primary pump (one on the left?) takes hot water from the boiler, supplies this to the thermostatic mixer, the mixed water is supplied at the required UFH temperature to the manifold pump (one on the right?) which distributes it to the UFH coils and some of this cooled water returns to the boiler with the remainder mixing with the hot water to give the required mixed water temp.
If you are correct in your understanding of the problem then suggest the following, can you see what the total flow is through the UFH manifold by the flow meters, if this is very low you may have a problem with the manifold pump, either a defect or a wrong setting, could also be the supply pump or the thermostatic mixer.
Can you confirm that the left hand pump is the hot water supply (boiler) pump and the right hand one is the manifold circulating pump and the settings on both pumps and the exact model(s) information.

Thanks John

No the left-hand pump is purely to circulate the water around the UHF system, the right-hand side one is the injection pump which pulls hot water in from the primary loop into the ufh system. Flow gages on manifolds are all showing flow around the system. This system works slightly differently, it's an injection system and there isn't a thermostatic mixer. What happens is that when the system calls for heat hot water from the high temp loop is injected into the low temp loop, with a back flow coming through a diverter valve.
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Savdefriz said:

Thanks John

No the left-hand pump is purely to circulate the water around the UHF system, the right-hand side one is the injection pump which pulls hot water in from the primary loop into the ufh system. Flow gages on manifolds are all showing flow around the system. This system works slightly differently, it's an injection system and there isn't a thermostatic mixer. What happens is that when the system calls for heat hot water from the high temp loop is injected into the low temp loop, with a back flow coming through a diverter valve.

Click to expand...

The Injector Pump is a Grundfos Alpha 2L and it is set on lowest constant pressure (I've tried it on highest). The other circulating is Grunfos UPS 25-80 180 and was on setting 1 (out of the 3).

Hi we we are ufh installers really need to see a wider angle picture that shows manifold as well as pumps . Also has system ever worked correctly?.

exedon2 said:

Hi we we are ufh installers really need to see a wider angle picture that shows manifold as well as pumps . Also has system ever worked correctly?.

Click to expand...

There are two sets of manifolds, and they are in different rooms (downstairs and upstairs). We inherited the system when we moved in to the house about 7 years ago and I don't think that it's ever worked properly. There is definitely flow going to the manifolds though as I 've checked the flow gauges to make sure the flow is balanced.

Savdefriz said:

Thanks John

No the left-hand pump is purely to circulate the water around the UHF system, the right-hand side one is the injection pump which pulls hot water in from the primary loop into the ufh system. Flow gages on manifolds are all showing flow around the system. This system works slightly differently, it's an injection system and there isn't a thermostatic mixer. What happens is that when the system calls for heat hot water from the high temp loop is injected into the low temp loop, with a back flow coming through a diverter valve.
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The Injector Pump is a Grundfos Alpha 2L and it is set on lowest constant pressure (I've tried it on highest). The other circulating is Grunfos UPS 25-80 180 and was on setting 1 (out of the 3).

Click to expand...

Had a quick look at the basics of UFH injector systems, one seems to inject hot water through the injection valve and into the circulating pump suction, the other seems to use the injection valve as a diverter to control the cold water return to the boiler. Your system looks a bit like the former? but afraid I can't make much sense out of it, Is that vertical pipe, the injector/diverter or what ??. and are the pumps pumping as indicated, or can you indicate. Thanks.

As John G has said difficult to make much sense of what you have! The valve you have circled looks more like a manual bypass than anything else .
Any chance or a picture of manifolds please?