I suspect that your system needs to be balanced, since it would appear that the majority of the water flow is going to the UFH.

@derek-m I can understand that, but with thermostats for each UFH room, wouldn't once they reach temperature then turn off and the water flow would be redirected to radiators anyway?

Posted by: @paulrlondon

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@derek-m I can understand that, but with thermostats for each UFH room, wouldn't once they reach temperature then turn off and the water flow would be redirected to radiators anyway?

I'm afraid that I cannot see your system from where I am sitting, you will need to provide more details of what is operating and what is not. How many water pumps and motorised valves do you have? Where are they located?

@derek-m I have 2x UFH manifolds with 2x heatmisers with 4x motorised valve (ground floor and upper floor). 2x motorised valves on the cylinder, 1x motorised valve per each 1x ufh and 1x heatmiser I have 1 water pump on the rads. The main rad flow pipe is hot. I've gone round all the rads, 3 of them have hot flow pipes, the rest are cold.

Posted by: @paulrlondon

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@derek-m I have 2x UFH manifolds with 2x heatmisers with 4x motorised valve (ground floor and upper floor). 2x motorised valves on the cylinder, 1x motorised valve per each 1x ufh and 1x heatmiser I have 1 water pump on the rads. The main rad flow pipe is hot. I've gone round all the rads, 3 of them have hot flow pipes, the rest are cold.

On the cold radiators, have you checked that both valves, one at each end, are not fully closed. Has your heating system been correctly balanced?

Are the correct water pumps operating and at what speed? Are the motorised valves open when they need to be?

You could try shutting down your UFH for a short period and see if any radiators get warm.

@derek-m As Derek says, the lockshield and ‘thermostat’ valves both need to be open, if they are now open and those radiators are cold, you one more thing to check and that is that they are full of water and not air. Having checked the valves, try bleeding out any air byt gently opening the bleed valve at the top of the radiator (situated at one end) but have a cloth ready to catch any water spurt; if you hear a lot of hissing… keep going until all the air is released and the water spurts out. If none of these measures help, you have blockages somewhere. If the three are all at one end of the run, this would indicate a blockage between the last warm radiator and the first cold one - likely as not, it will be on the feed rather than the return pipe. Regards, Toodles.

The flow of 40 and return of 29 is a dT of 11 which is very wide for an Ecodan, they try and hold to 5, if it can't then more heat is being sucked out than it can put back in.

What is the pump speed on your ecodan controller its under the settings menu on the far right labelled pump speed, I find that 3 works for my system but with everything calling for heat the dT will be 6-7C.  Its a balance of performance and noise speed 5 is quite loud depending on location of your system.

If some rads are cold and opening the valves on them doesn't help, you could try increasing the Ecodan pump speed on the controller to 5 and see what happens. 

As also suggested the pump speed for your radiator circuit may be too slow meaning all the heat is taken by the first rads in the circuit.

Posted by: @paulrlondon

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@derek-m I have 2x UFH manifolds with 2x heatmisers with 4x motorised valve (ground floor and upper floor). 2x motorised valves on the cylinder, 1x motorised valve per each 1x ufh and 1x heatmiser I have 1 water pump on the rads. The main rad flow pipe is hot. I've gone round all the rads, 3 of them have hot flow pipes, the rest are cold.

Have you resolved your problem? Feedback is always welcome.

So I bled the radiators, I switched my programme back to fixed flow 40C and within 12 hours all radiators were hot again. So there's no blockages. I have then since discovered separate issues which may impact things, actuators on manifolds were not tight so they weren't actually turning UFH rooms off and on as they reached temp, so in effect stealing heat. That may have been the problem, the ASHP unable to keep up with the constant heat demand from UFH during the cold snap where we were at 0C. But it's only a theory. I'm going to leave my programme on fixed flow 40C for the next 0C spell which I think is tomorrow night and see if the radiators stay warm. If they do ill go back to weather compensation and try tweaking that, otherwise im concerned my ASHP just isn't able to deliver enough heat for the whole system.

@paulrlondon this sounds to me very much like a flow balancing issue, as the others are suggesting. Its not an "ASHP can't deliver enough heat" issue . get the flow balancing right your house will be warm and your ASHP will be as efficient as it can be.

Posted by: @paulrlondon

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I switched my programme back to fixed flow 40C and within 12 hours all radiators were hot again. 

its should take a few 10's of minutes at most, to feel warmth in all the emitters , in a balanced system.

Hypothesis, based on your two described behaviours:

1. By running at the higher fix flow temp, you are using the UFH's actuators as a "non-ideal" means of flow balancing  i.e. eventually the UFH zone will close down because its hot enough, and  then (and only then) does the flow want to go to the radiator zone. flow flip-flops between the two. Not ideal, but keeps you warm.

2. in weather compensation mode with the lower flow temperature, the UFH zone may never shut down as its always wanting "just a bit more" heat, it takes all the flow, nothing left for the radiators.

running in fixed WT mode keeps your house warm so a valid workaround for now, but it will cost you lots more to run, so there are three possible solutions to investigate:

- increase the radiator pump speed. this might be enough to get the flow to to round the radiators at the same time as the UFH is active.

- If some radiators are hot and others are not, partially close the lockshield valves on the ones that warm up first / most quickly, until the cold one gets some warmth. This is a trial and error process. Keep notes of how many turns you do, you will forget.

- BEST OPTION: Consult with your installer about how the UFH circuit and the radiator circuit have been balanced so that they both get their fair amount of flow.  If they say they didn't do this, ask them to do so and remind them that balancing is part of the proper commissioning of any heating system.