gck303

Thank you very much. They were not quite 100% open. I fully opened the valves and the noise changed slightly and the flow picked up. I am now upto 16-17 l/m when heating the DHW!!! Is this what you would expect with two 15-50/60 pumps running at 'III' with 22mm pipework? Is still seems slow. The ASHP says the max from rate is 25.8 l/m. Or, am I hitting the limits of the 22mm pipework?

A further thing I have just noticed.... When it is heating the DHW the flow rate is still only 14l/m. This is all in 22mm copper pipe to/from the ASHP, so should I expect that the flow to be greater? There are two -15-50/60 pumps set on 'III' so it should be going mcuh quicker! If with a relatively unrestricted flow into teh DHW tank, then it would not be sensible to get a greater flow into the rads. Does this suggest that there is a blockage somewhere?

Which manifold? I do not have a manifold in the system, yet.

I will check this. Thanks. I have never done this before, but it is quick and easy. And TBH something and on reading up something I should have done before I wrote this message. Once I have drained down the system, and put in the pipes and then repeated it to remove them all it might not actually be that much extra effort. The temperatures are low, a good few degrees beneath what they should be. High thirties, rather than the 44 coming of the ASHP. And those few degrees do make a difference.

Yes, I have bled the radiators. If that is what you meant...

You mean unplumb the dodgy radiator, put in some temporary pipe work, and see if that helps? Yes. I could do. I would need to connect it to the existing system somewhere. I was thinking that a radiator manifold near to the main pumps would allow me to do exactly this and give me total control over the problematic radiators. Does that sound sensible?

Yes, this is almost correct. - There are a number (2) of radiators that are fully open (TRV and lockshield) which are not getting flow. - The other radiators (10) are almost closed and getting enough flow. If they are closed any more, then they shut of entirely

It is a 15-50/60. There are two pumps of identical size, one saying it is running at 18W and the other at 34W. I think it is in radiator & 'max' mode. I have cranked both pumps upto III. Then are both showing 34W on the display. The flow is up to 12.5 l/m.

The 10 l/m is measured and correct. I need to increase this flow to 20 l/m. The radiators are warm. But at the two that are at the far ends of the house are not warm enough. They are a few degrees cooler than the others. At 12 l/m there is not enough flow for all the rads. Some are warm enough, others are not warm enough. The warm ones have their lock shields almost closed, the cool ones are fully open. It is not going via a bypass rad. If it was, then the temperature drop would not be low enough. It is correct as having a 5C temp drop.

8.5kw. Which is adequate, as it is delivering that heat continually. Selecting an ASHP is a fine balance, as you want to neither over or under spec it. It is a 8.5kw unit and capable of deliverying a greater output, but the flow is not great enough to take the heat away from the ASHP. How can I increase the flow? Is 20 l/m an reasonable flow for 12 radiators?

Thanks. All of the suggestions have been considered and have either been tackled, or cannot be tackled: - the radiators have been balanced, the problem remains. - the system was flushed when the ASHP was installed. But, it is an old system. Crud may remain. - the pipework is a mix of 22mm and 15mm pipework, but it missing much insulation under the suspended wooden floor. Getting to it is impossible as it would require lifting the Amtico, hence my thought to lay new pipes running direct from a manifold. - I have a decent IR thermometer and am monitoring the flow/return at the ASHP. The issue is the overall flow. I am wondering if the biggest issue seem is the poor overall flow. I would expect that a heating system would have a flow of 20+ l/m, the pumps are running consuming 54W and there is 6m of head, but only shifting 10-12 l/m. Surely this is a problem? With an ASHP the flow is critical, I ideally want to get 2 l/m though every one of the 12 radiators in the house. Eg with a 42C flow and 38C return. You need to have a high flow rate, so that the difference between the flow and return can be minimised, allowing to to reduce the flow temperature and increase the COP.

I have a older 5 bed brick house (Edwardian Terrace) with a new ecodan ASHP heatpump installation. We run it 18+ hours in the day with a flow rate no greater than 45 C. We have c. 10 radiators. I have read the voltage from the Sika Vortex (flow sensor for ASHP) and I am getting a flow rate of about 12 l/min. When calculating the temperature difference and the power output, I get a reasonable COP of 3 ish. This suggests that the flow rate is correct at 12 l/min. The radiators on the ground floor that are furthest from the main 22mm circulation pipes have their lock shield valves fully open and just do not seem to be getting enough flow. Most of the radiators are nearly closed, the problematic ones are fully open. Still these two do not get warm enough. OMG. How can the flow rate be so slow? I have two circulation pumps consuming 50W, so there is not an absence of pressure. One of the pumps is a Grundfos ALPHA3 which shows a head of 6m and also shows a similar flow, of 0.6m/h. What to do? Replacing any of the pipework on the ground floor is a major exercise as we have hard floorings everywhere. I am wondering if installing a radiator manifold and putting new Speedfit pipework in for these radiators direct to the manifold is a sensible way to proceed? https://emmeti.co.uk/products/heating-manifolds/ Thanks, George