Mixing Pressure Problems

John.g · Nov 30, 2020

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??,

Savdefriz · Nov 30, 2020

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.

John.g · Dec 1, 2020

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.

Savdefriz · Dec 1, 2020

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!)

John.g · Dec 1, 2020

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.

exedon2 · Dec 1, 2020

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

John.g · Dec 2, 2020

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.

Savdefriz · Dec 2, 2020

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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exedon2 said:
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!!!!

John.g · Dec 2, 2020

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.

Savdefriz · Dec 2, 2020

It's getting warmer.. I'm touching nothing.

Mixing Pressure Problems

John.g

Savdefriz

John.g

Savdefriz

John.g

exedon2

John.g

Savdefriz

John.g

Savdefriz

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