Having a nightmare commissioning my ASHP with twin UFH manifolds

[blankton]

Hi. I am currently renovating an old cottage. I've fitted wet UFH upstairs and downstairs. I was advised to have one manifold upstairs and one downstairs to reduce the chances of air locks, so this is what I did. At present it is effectively one big heating zone. I had also read advice against having lots of zones, so I am going to try and just balance the heating of the single zones, by playing with the flows. 

 

I've fired up the system and while the top floor manifold and blending valve seems to work as it should. The bottom floor one isn't. There is no flow at all occurring downstairs, either in the primary circuit down to the manifold, or through the UFH loops. Here is a schematic:

 

I've messed about with quite a few things:

- if I pop off the UFH loop return from the manifold I can get flow through that loop (albeit with the water going all over the floor)

- If I use the "cold" drain valve, I can also get flow (again with the water being lost from the system. 

 

 

When I do both of the above, warm water is drawn down the primary circuit towards the blending valve. 

 

- I've also bypassed the ground floor setup, this results in the flow round the primary circuit, so this external pipework seems ok. 

 

The  manifolds are cheapish things from an online store. I fitted one in my current house 15 years ago and it has never skipped a beat, which is why I went with the same again.However, in my current house I only have 1 manifold and radiators in the rest of the house. 

 

My current thinking is either I have a rogue faulty manifold, or the way I've piped them up in series is causing some weird back-pressure effect. Should I perhaps of put a check valve between the 1st floor return and the ground floor return, to prevent the first floor return from applying a pressure to the "wrong" side of the mixing valve?

 

 

I should also add that I've filled each loop one by one using a hose through the drain valves on the manifold and I've also tried switching the flow and return on the ASHP, in case the flow and return on my Chinese manifolds was the wrong way round. 

 

Sorry for the long post.... I've spent 3 days poking about at this, probably longer than it took to pipe it up in the first place! I'm hoping that I've done something fundamentally wrong with piping the manifolds in parallel and it will be instantly obvious to anyone in the know. 

 

Next thing I am going to try is getting rid of the pump and blending valve from the ground floor UFH and just put the flow and return straight into the respective manifolds. Since I brought the blending valve and pumps, I've since read that they are not really necessary with ASHP due to the lower flow temps. 

 

edited to sort photos. 

Edited January 1 by blankton

[blankton]

double post due to image issues. 

 

Edited January 1 by blankton

[sharpener]

?Somethng wrong with the ground floor mixing valve or you have got the connections to it transposed?

[akjos]

I have a similar setup, two UFH manifolds, on on ground and one on first, same piping as you but without any mixing valves and pumps on the manifolds. The ASHP flow and return are directly piped into the manifold as the internal ASHP pump has enough power in my case to push flow through everything.

 

If you remove the mixing valves and still don't have flow in the ground floor manifold, try closing of the first floor one and check again. Water will take the flow of least resistance, so it might be the case that your first floor manifold just passes the whole flow through, so you'll need to add resistance so water reaches the second one.

 

This should have been calculated as design though, and if all flow rates for each loop are correct this shouldn't be a problem. Worth checking though.

[dpmiller]

are the manifold isolators actually opening correctly?

[mk1_man]

I have ground floor manifold covering 150m2 and a 1st floor manifold covering 100m2 and it works great. Primary difference is that I don't have mixer or pumps on the manifolds since installing the ashp and it is much better than when I was running on boiler with the mixers.  Simpler is the way forward and also much quieter 🙂

 

[Beelbeebub]

Usually the manifolds have Isolators on them.

 

Have yountried isolating the 1st floor manifold and checking if thr downstairs one works in that situation?

 

My gut feeling is the mixing valve or pump on the ground manifold are the issues.

 

First check the pump is actually spinning. It should get warm and vibrate a bit. You can check it is turning directly and free it up if it's a bit seized following this video

 

If the pump is turning then you should get flow (as shown on the flow indicators). If not check the actuators are opening and that your balancing valves are open. The flow meters are also the balancing valves.

 

If there is flow but it's not getting warm then it's your mixing valve. Try winging it back and forth abut to free it, otherwise get it replaced

[blankton]

Thanks for the advice. I set about deleting the blending valve and pumps today and the issue became obvious........ 

 

I'd ordered 2 identical kits and built them up on a bench. There should be a non return valve between the blending valve and the hot manifold, on the bottom (cold) manifold this non-return valve should not be there, with just an open union to fill the space where the non return valve is located on the top manifold. 

 

I had used both non return valves on one manifold and both open unions on the other. The manifold with no non return valve (top floor) worked fine. Not surprisingly, the one with an entra non-return valve, which was pointing the wrong way, didn't work 🥴

 

 

[dpmiller]

that'll do it...