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Discuss Mixing Pressure Problems in the Central Heating Forum area at PlumbersForums.net

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It may but last night I was looking at the system schematic and can't figure out why the injection pump inlet is taken from the boiler return (NRV in boiler flow), this means that if no demand for DHW or radiators that the injection pump, is fighting the boiler circ pump (which is on the return), very UNlikely designed that way, have another good look at the arrow on the injection pump which may be pointing upwards, the pump would then be returning cold water to the boiler but then there would need to be (probably controlled ) a hot water supply to the UFH main manifold somewhere, if you look at the schematic which includes the DHW cylinder you will see some form of controller that looks a bit like a pump but is probably a controller as it seems to be wired into the kanmor? high up in the drawing, can you identify this as well this evening.
 

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Right then John what do you want? IMG_20201130_165133.jpg
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The only thing missing from the schematic is the outdoor sensor which I think that the unit uses to calculate the flow need to keep the house at a certain temperature. I've also changed the alpha pump settings to lowest constant flow (I) and that seems to be letting the hot water flow through from the primary circuit.

As for the flow, here's my hypothesis:

The primary circuit has two junctions, the first is the intake and the second the return flow. I'm assuming that if the pressure of the return flow is greater than that of the primary the hot water will take the path of least resistance and flow downwards to the injector pump. This seems to be what's happening in practise, as if the return flow is too fast the hot water never gets to the t junction. If it's too slow, the injector doesn't allow any water to be injected which could be due to the incompressible nature of the ufh circuit, or just because the path of least resistance is forwards rather than down.... (I need a degree in fluid dynamics for this one!)
 
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Arrow is definitely pointing down. Pages as requested, but I don't know what I've done but the mix temperature is going up. It's at 27 now and rising and it's never been above 21. Basically I put the alpha on (I) waited until primary was sending warm back to the boiler, changed to the pump up to highest constant and it seems like it's working 🤯
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Just checked again and it's back to 24 but progress.... I suppose it's proof of concept at least.
 

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Thanks but can't read the attachments.

What do you mean by
" waited until primary was sending warm back to the boiler "

Is/was the CH or/and the HW on while taking these tests?

Can you see what that item is in the picture showing the cylinder, above. (post 21)

I honestly cannot see that system working as is with the NRV installed where it is and without the CH or HW on as well, at best then IMO, the injector pump will take some of the cooled water returning from the rads/cylinder coil and inject it into the manifold but that temperature is completely dependent on that return temperature which may be even lower than the required UFH temperature, also the "bypass" is stationed far too close to the injector pump to give any real temperature or contra flows separation.
Can you have a quick read through those pages and see what commissioning problems they had and a explanation of how the system is supposed to work.

Taking the injected water supply from between the NRV and the boiler would definitely make some bit of sense as it is then hot injected water at a set (boiler) temperature.
 
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I've tried to annotate the picture to label each item.

Hope this makes a bit of sense.

Water.jpg
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Thanks but can't read the attachments.

What do you mean by
" waited until primary was sending warm back to the boiler "

I just meant that I restricted water flow through bypass so that the return to the boiler heated up.

Is/was the CH or/and the HW on while taking these tests?

I hadn't switched anything off

Can you see what that item is in the picture showing the cylinder, above. (post 21)

Wasn't sure what you meant so I annotated the original photo

I honestly cannot see that system working as is with the NRV installed where it is and without the CH or HW on as well, at best then IMO, the injector pump will take some of the cooled water returning from the rads/cylinder coil

No rads and cylinder coil has its own NRV as shown

and inject it into the manifold but that temperature is completely dependent on that return temperature which may be even lower than the required UFH temperature, also the "bypass" is stationed far too close to the injector pump to give any real temperature or contra flows separation.

The contra flow separation proximity is what I thought the problem was.

Can you have a quick read through those pages and see what commissioning problems they had and a explanation of how the system is supposed to work.

Taking the injected water supply from between the NRV and the boiler would definitely make some bit of sense as it is then hot injected water at a set (boiler) temperature.
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Here's the scanned pages.
 

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Can you take a snapshot on the left around where I have continued the red line showing the pipework layout, in particular any NRV (the ones you showed are motorized zoning valves)

Read the Tap scanned pages, the most important item now is to see where (if) this NRV is.


UFH Pump Injected System near Cylinder rev1.jpg
 
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I think that's about as clear as you can get it, there isn't a NRV between the T off for the HW cylinder coil and the motorised UFH zoning valve so that means that the hot water is supplied to the UFH once its opened despite the original drawing showing one, I wonder why?.
So, as you said the proximity of the injection pump and by pass vale is the main problem although I find it inexplicable that a system would be designed this way... it may work if mods made as in attachment, I don't see any reason to have the hot & cold looped as this only creates a full fledged by pass once the UFH zone valve is opened, also the original injection pump was a standard pump which can be speed controlled. UFH Baxi rev1.jpg
 
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Thanks again John,

I've restricted the flow on the bypass valve and turned the Alpha down to constant setting (II). I'll see if that's enough flow to get at least a little bit of heat into the system. I was also wondering if an auto bypass valve might help.

As you know a bit about pumps do you think this one would be suitable as the documentation says that the original was a grundfos 15-50.


I just can't find out if it's controllable.

I'll speak to my heating engineer and see if he can make the relevant changes (although he's the one who put the alpha on!).

Thanks once again for your help with this enigma! One day I will get it to function correctly
 
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No, I don't think that pump is compatible with the controller, I wouldn't be too worried about the actual speed control just now, if you and your engineer thinks the mods may work then just do them first. It may be beneficial to install a ABV in the system.
When did he fit this Alpha??,
 
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I moved in to this house about 7 years ago. The UFH has never really worked since we moved in.

I think that as it wasn't working he swapped the injection pump about 5 years ago when he changed the boiler.

The system had a dutch boiler and Danish manifolds. Essentially each year we just swap the pieces bit by bit for things that are actually recognised in the UK.

To be fair to our hearing engineer, everything was pretty much non standard and so trying to pin down the problem was a nightmare.

My initial thoughts were that he had over pressurised the UFH when he replaced my downstairs manifold so a week ago I started doing my research. Then I thought it was the bypass valve, but I didn't know enough to be sure. I think my wife thinks I'm having an affair with the boiler as I've spent so much time in that room "fiddeling". Turns out I actually might have been right lol. Thanks once again.
 
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Just re thinking suggested mods, suggest just relocating by pass and isol valve but do not remove the return loop to the boiler as high risk of too low circulation flow through the boiler if UFH only on.
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Back for more punishment, I think that rather than a PRV in the by pass that a two port Tapstat might give far better control, you can attach the sensor to the return (or the mixed flow pipe as desired) and it will/should then control to the requiredtemperature. If you install another isol valve in the by pass you can then isolate it and install/change to which ever device gives the best results.
 
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Evening John, It's the enigma that's more puzzling than a Rubik's cube.

I think that whatever you put in there, it's always going to be too close to the injection feed. I've been playing around with it today again and as long as I keep the Grundfos Alpha on it's lowest setting I do get hot water to flow just not enough. Problem is that I'll never get enough if I'm that close to the injector because more water will always equal more pressure which will inevitably mean feeding back into the injector loop. (Managed to get the mix feed up to 31 degrees today a new record, although it only stayed at that for half an hour).

Next enigma is trying to get a heating engineer to come and sort it out before the snow hits, and it's a bit of a trek from the south of Ireland to the North of England...

I'll keep you in the loop (Oh the puns!)
 
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Any of the drawings refer to the bypass as just that..... a bypass and it would appear to be just that, ie, a bypass for the injector pump. If there were no injector pump fitted then now that we know there is no NRV fitted, that bypass IMO would supply almost ample flow from the boiler circ pump bearing in mind that it only has to supply only ~ 25/35% of the mixed flow. NO where is there any mention of cold water return to the boiler which is just as important as any injector pump or whatever so was something forgotten in the whole design.
Maybe at the end of the day thermostatic mixing is the real answer?. So, yes, heating engineer or magician needed.
 
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I've watched this thread with interest im still sure only real cure is in essence to convert manifolds to standard pump/blender layout its done that way because it works!.
If its what you want flow temperatures double what our achieving would be possible
 
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Just putting on my magicians hat but i think this will probably work.

Remove the return loop as there is no more risk of the boiler having insufficient flow with this proposal than with the pump/blender route.

So, remove return loop, leave existing by pass as is.(shut)
install new return piping Teed as far upstream as possible on the cold return and connect into the return to the boiler at the now broken loop with isol v/vs at both ends.
Install tapstat (injector valve) in this piping and connect sensor to the mixed water line or the cold water return as required.
I think this has a good chance of working as the hot water will be taken in by the manifold pump and the cold water return by the boiler circ pump via the controlling injection valve.?
You might even be able to run with no injection pump if on UFH only

The attachment shows the injector pump pumping into the manifold discharge unlike this set up.

Injection Valve Return.gif
 
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1606937688400.png

I was thinking that this might be the simplest fix. Just cut the bypass pipe, loop it out and put a t junction back in to the pipe pretty much directly above where it is at the moment. That will mean greater distance between the injector and the bypass returning the cold, meaning that less cold should flow back. I've left the Grundfos on (I) and the mix is heating up but it's a really big system (I think there's about 1600m of underfloor piping in the house). I'm hoping now that the answer might just be as simple as put the pump on a lower setting!
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I've watched this thread with interest im still sure only real cure is in essence to convert manifolds to standard pump/blender layout its done that way because it works!.
If its what you want flow temperatures double what our achieving would be possible
Glad that you've enjoyed the Craic... You may be right, but I'm never going to get that sorted before Christmas! I feel like I'm getting somewhere but as I said to John earlier, everything in this system is nonstandard and I'm just a man with no knowledge of plumbing trying to figure it all. Let's just say that if I was putting this in from scratch I probably would have chosen something a little more "standard". I'll invite everyone to come and have a look once things get back to normal!!!!🤣🤣🤣🤣
 
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IMO, whatever else, you will definitely have to break the link between the flow and return.
Why don't you just switch off that injection pump just now and see if any improvement, there should be sufficient head from the boiler circ pump, the water will still flow through the stopped injection pump and it will now not tend to pull cold water back into the system.
 

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