It should make zero difference if on the return or supply pipe. Convention always puts the pump on the lowest temperature side of the system.

I quickly did a Google search and the first image I found was this, with the pump on the pump on the return side

Hi

It does not matter which side the pump is on, it is a circuit. You must however make sure that you have enough open zone system volume and flow. You will need at least 50 liters of open zone system volume. A single panel radiator, 0.6m high and 1 m long will hold about 3 liters, if you do not have enough, you may need to get a volumisor and install it on the flow, not the return. Remove all control from all common area radiators and only control your bedrooms. If possible, move the controller to the hall or somewhere where it is not influenced by other heat sources. As you are not controlling the Delta T, your flow rate must be about 14.5-15 l/min (For your 8 Kw unit), no more. You may need 2 pumps to achieve this but try with 1 first.

This should work well.

Brendon

@johnmo Thanks, I hadn't seen that set up diagram before

@heacol Thanks for the info. I've currently hot 48 litres in my radiators, so a bit below 50 but the documentation for Samsung 8kw says 30 is the minimum, so I think it should be okay. Also I'm planning at least one new radiator and one swap to a largeer one. 

I've got a pump with variable speed, so I think I can adjust that to get the right flow rate once I've made the changes. 

Posted by: @ecobaker

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Samsung 8kw says 30

That's really for defrost support. 50L would be to limit short cycling. More volume the better and will lead to longer cycle times and overall better CoP.

Have you considered leaving the LLH there? It provides a point to remove air and catch debris. Just plumb across the flow side only. So remove secondary pump and return connections from the low loss header and allow the return to by pass around the LLH. Leave the flow connected.

Less work, add some volume, retain air bleed and debris catcher. No loss of efficiency, one pump removed.

Posted by: @ecobaker

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I've got a pump with variable speed, so I think I can adjust that to get the right flow rate once I've made the changes. 

The Samsung Gen 6 supports Pulse Width Modulation control of pump speed if you have a pump that supports it, so it sets the speed that is most appropriate at that particular time.

I made a mistake of initially buying the wrong pump, but rectified it later and it works well now. My blog for April 2023 describes a lot of the things to look out for if you want to go down that route.

https://thegreeningofrosecottage.weebly.com/blog/archives/04-2023

@johnmo I had considered leaving the LLH in, but wouldn’t it be best to by pass the flow and leave the return connected to it for catching debris from radiators? 

My other option was to take it out completely, but add an automatic air valve at the highest part of the pipe work and a mag filter on the return to the heat pump. 

@bontwoody I don’t have the PMW control pump just the Auto with the ability to adjust the flow rate on the pump. Changing it to an PMW pump is on the list, but a bit further down than a few other things. I’m going to manualy adjust the pump I have once the set up changes have been made and see what performance I get. I’ve got at least one radiator adjustment to make as well before the pump gets changed. Thanks for the blog posts, lots a great info there.

@ecobaker Your system volume will be fine, just make sure you get the right flow rate with all TRV's open and at least 8 l/min with all closed. Leaving the LLS header in is an option but on the flow. It will benefit you more there. Some older GEN 6 controllers do not have the software for PWM pump control, running a slightly lower flow rate than peak optimum is a good compromise but not as good as PWM.

So I made the switch of pumps and took out the LLH (also added a magfilter) the pump I put in is a ump3 flex 15-70 130, got it all wired up and the system working.

The problem is, although COP is fine between 4.0 and 4.1, I'm getting a lot of cycling when the heating is on, and two radiators on one branch of the heating are not getting hot. Could this be an under powered pump? Maybe I could try taking the PWM cable out and just running the pump at full speed. According to my flow meter I'm getting 18 - 19 l/m when it's operating. 

@ecobaker if you are sure that the two radiators dont have an airlock, then it might just be a matter of balancing all the radiators to ensure that they all get adequate flow. The cycling is probably due to not being able to lose enough heat from your radiators for the heat pump to be able to run at its lowest setting. Getting the two radiators working will help that but you may have to look at raising the flow temperature slightly if it still occurs.

Ive played around quite a bit in my blog and have now just about got it working as I want.