Drop in Flow Rate

[LA3222]

Right, I have a little puzzle going on which some on here who know more about UFH than I do can shed some light on.

 

The manifold for downstairs - when I close the thermostatic mixing valve the flow rates through the loops increases but when I do that the flow temp drops. So I want to open it up to increase the temp to around 30 degrees but it strangles the flow - what the hell is going on?

 

The upstairs manifold - when I open the thermostatic valve up the flow rate increases ..... the opposite effect to downstairs.

 

What is it that the pump doesn't like on the downstairs manifold?

[JohnMo]

Photos of your manifold, pump and mixer, would be helpful.

 

When you say close the mixer - do you mean reduce temperature or increase temp?

 

Are they the same mixer valves?

Do you have a pump on each manifold?

 

[dpmiller]

Are the flow and return from the heat source reversed?

[Nickfromwales]

13 minutes ago, dpmiller said:

Are the flow and return from the heat source reversed?

First thing to check. Turn the system off, let it go 'cold' and then switch on at max. See which of the flow and return pipes get hot first to eliminate reversed flow to one of the two manifolds.

Opening the TMV's should increase flow on both, so something strange going on there.

[LA3222]

Right, I need to get back to trying to unpick what the issue is with the flow rates of my ground floor UFH.

 

I can get the flow rates to increase to what I would expect, but at the expense of temperature – will explain further on.

 

Whilst looking into this issue (or trying to online) I stumbled across a thread where I had made a comment about my flow rates being good – suggests this a relatively recent phenomena (not identified until the heating season kicked in)

 

Both manifolds are Ivar Unimix C and there are no fault codes showing on the manifold pumps, seem to be working ok.

 

Fault Finding

 

There are two manifolds, approx. the same size – ground and first floor. The pipe run to the first floor is shorter than that to the ground so my initial test was to turn off the first floor manifold to confirm it was not stealing the flow. This made no difference to the ground floor flow rates.

 

Next I turned up the pump between buffer/manifold and on the manifold itself to max – made very little difference to flow rates.

 

Test Conditions for manifold behavioural comparison

 

TMV removed so the flow temp was pretty much what the ASHP was heating the buffer to – approx. 31 degrees. Primary and secondary valves closed on both manifolds.

 

First Floor Manifold

 

Open secondary bypass fully:    flow rate drops very slightly, flow temperature remains stable.

Close secondary bypass fully:    flow rates increases slightly, flow temperature remains stable.

 

Open primary bypass fully:         flow rate drops very slightly, flow temperature remains stable.

Close primary bypass fully:         flow rates increases slightly, flow temperature remains stable.

 

Close primary/secondary bypass, re-fit TMV and leave fully open: flow rates and temp are good  

Close primary/secondary bypass, re-fit TMV and set to 30 degrees: flow rates drop slightly, temp ok

 

Conclusion – the first floor manifold appears to function correctly.

 

Ground Floor Manifold

 

This is where things get strange:

 

Open secondary bypass fully:    flow rate shoots up, flow temperature tanks down to 25 degrees.

Close secondary bypass fully:    flow rates tanks, flow temperature goes up to 31 degrees.

 

Open primary bypass fully:         flow rate shoots up, flow temperature tanks down to 25 degrees.

Close primary bypass fully:         flow rates tanks, flow temperature goes up to 31 degrees.

 

Close primary/secondary bypass, re-fit TMV and leave fully open: flow rates crap and temp is good  

Close primary/secondary bypass, re-fit TMV and set to 40 degrees: flow rates shoot up, temp drops to 25 degrees.

 

Conclusion – the ground floor manifold is not quite right!

 

Problem:

 

It looks to me like the hot flow is being choked in the ground floor manifold affecting flow. There appears to be enough flow for the pump to keep working (no error codes), but not enough flow to get a good volume of warm water pumping around the UFH loops.

 

This is supported by the fact that when either of the bypass valves on that manifold are opened the flow shoots up – however this kills the temperature of the flow as the hot feed is being heavily supplemented by the cold feed, killing the overall temperature.

 

Is it normal for the hot side of the manifold to get choked/clogged? Could something else be going on? @Nickfromwales @PeterW, gents if you can shed some light it would be appreciated. 

 

Looks like I need to take it apart but that is in the PITA box at the minute!!

Edited December 11, 2022 by LA3222

[JohnMo]

Questions

Are you running this on a single pump between the buffer and both manifold mixers, or do you 3 pumps, one on each of the manifolds and another at the exit of the buffer?

[LA3222]

5 minutes ago, JohnMo said:

Questions

Are you running this on a single pump between the buffer and both manifold mixers, or do you 3 pumps, one on each of the manifolds and another at the exit of the buffer?

Three pumps. One on each manifold, one more to pull/push from the buffer to both manifolds.

 

Plenty of pumps. Upstairs manifold is identical size/setup to ground floor manifold and works fine. The ground floor one don't seem to play ball🤷‍♂️

[JohnMo]

Is there any hydraulic sepereration between the pumps?  The buffer would normally be the hydraulic sepereration, the manifold pumps pulling/pushing from the buffer.  The one in the middle of the buffer and UFH pump may be the issue 

 

It could be you have too many pumps.

 

Can you switch of the buffer pump and see what happens?

[LA3222]

14 minutes ago, JohnMo said:

Is there any hydraulic sepereration between the pumps?  The buffer would normally be the hydraulic sepereration, the manifold pumps pulling/pushing from the buffer.  The one in the middle of the buffer and UFH pump may be the issue 

 

It could be you have too many pumps.

 

Can you switch of the buffer pump and see what happens?

I dont think the pumps are the issue. When I completely shut upstairs down it had no effect. Just turned the buffer pump off and no effect other than to reduce the flows slightly - so worse. 

 

The key thing for me is the effect that opening the bypass has - I may be reading this wrong but the flows shoot up and in my mind what's happening is that the flow coming through the hot inlet is crap, when I open the bypass it supplements this flow with recirculated cold and then the pump shoves all that round the loops. This kills the temp though.

 

Not sure why insufficient hot would be going through the pump to the loops - a blockage in the manifold?

[JohnMo]

On the Ivar mixer, the part that connects to the hot part of the manifold has an integral isolation ball valve, have you checked this is fully open?  Needs an Allen key to move I think.

[LA3222]

52 minutes ago, JohnMo said:

On the Ivar mixer, the part that connects to the hot part of the manifold has an integral isolation ball valve, have you checked this is fully open?  Needs an Allen key to move I think.

Yeah, no dramas there. This has been up and running for over a year now....pretty sure it was fine in the last heating cycle - the issue seems to be a recent developement

[Nickfromwales]

I've just been called to a clients build where the Ivar blending valve is not letting the toasty hot water in the flow pipe to it, through to the loops ( even with the white TRV style head removed from the mixing valve. I drained down and removed the cartridge and it was firmly stuck, but in the fully open position!! I serviced the valve, proving free movement and that the pin returned to its "sticky-outy" position ( returned to that position by the spring ) and reinstalled it all. Set it to work, and fark all, still just a steady 20oC of heat which was keeping the dwelling at too low a temp.

This setup has the ASHP pumping into a LLH and that is immediately adjacent to the UFH manifold / pump etc, so never needed a secondary pump to get from the LLH to the manifold.

Conclusion, possible knackered mixing valve.

I'm going to order a brand new one and install it as this is an inconvenience to my client, but this worked very well the first 2 winters, and I'm flummoxed as to why this has given up the ghost ( where others have been in elsewhere, longer, and are still working perfectly!?! Some houses I've fitted with 2x Ivar manifolds and still zero issues on those projects.......

 

Could this be a few stray "Friday afternoon" valves perhaps?

[LA3222]

On 11/12/2022 at 19:20, Nickfromwales said:

Could this be a few stray "Friday afternoon" valves perhaps?

Certainly looks that way!

 

Is this the badger?:

 

 

[Nickfromwales]

10 hours ago, LA3222 said:

Certainly looks that way!

 

Is this the badger?:

 

 

Looks different to the one I removed, but may be un upgraded replacement part?

[Nickfromwales]

2 minutes ago, Nickfromwales said:

Looks different to the one I removed, but may be un upgraded replacement part?

 

👎 Prior to 2014??

[LA3222]

48 minutes ago, Nickfromwales said:

 

👎 Prior to 2014??

Rog - didn't notice that bit!

[MRH1234]

I possibly have a problem with my Ivar unimix mixer and just wanted to understand the primary and secondary bypasses better.

 

Does the primary bypass have no use with an ASHP setup and can be set to minimum/closed?

 

And what is the use of the secondary bypass, is it setting the amount of flow from the return that can go back in to the send flow? And therefore its for setting a range the actuator can work over?

[JohnMo]

Why not download the instructions?

 

Primary bypass is important, with a buffer you need a balanced flow either side of the buffer, without a buffer you have to maintain a minimum flow to keep the heat pump happy. Primary bypass in a min flow valve. Secondary is how much mixing occurs between incoming hot water and return water.

[MRH1234]

Hi, yes I did look at the manual, but to be honest it wasnt clear to me what they were doing. I have a buffer tank, so the next question is how would I balance either side of the buffer? I have 2 manifolds and they both have the send to them and return all be it 10-15m apart. They are not casacaded ie ones return feeding the other which I believe can be the case.

 

My theory was the primary bypass wouldnt be needed as if the ASHP has a demand then there would be flow and if not then the pump would be off anyway and bypassing back a percentage of your hot water back to the tank will only lose heat on its trip round and this would be better just going round the manifold loops that was calling for heat.

 

I have to assume the installers didnt touch either primary or secondary.