@derek-m Thanks for the feedback, the buffer tank was recently fitted in place of a low/loss header tank (think that's the correct terminology). I will record the pipe temperatures and come back to you.
Looking at the schematic, this is how I suspect your system will be operating at the moment, though please correct any incorrect assumption I may have made.
When one or more of the room thermostats calls for heat, the relevant heatmiser should sense this and open the relevant solenoid valve on the relevant manifold. The heatmiser should also start the relevant Grundfos pump and open the relevant Honeywell zone valve. A signal should also be sent from the heatmiser to the heat pump controller to start the heat pump.
Water should be drawn from the main flow manifold and pushed through the relevant UFH loops and flow to the main return manifold. The water supplying the main flow manifold will be drawn from the upper outlet port on the buffer tank, with the water from the main return manifold flowing back to the lower inlet port on the buffer tank.
The warmed water from the heat pump flows through the ESBE valve to the upper inlet port of the buffer tank, with the return water flowing from the lower outlet port on the buffer tank, via the Sigma filter and main water pump back to the heat pump.
The system therefore contains two individual, though interconnected, water circulation loops, one from the heat pump, via the buffer tank, filter and water pump and back to the heat pump, and the second one from the buffer tank, through one or more UFH systems and back to the buffer tank.
For correct transfer of thermal energy from the heat pump to the UFH loops, it is therefore necessary to balance the water flow through the buffer tank.
Whilst you are collecting the temperature measurements could you also note the speed settings of the various water pumps.
Also check around your system for any small Automatic Bypass Valves.
I have attached the schematic with the relevant info as suggested previously, I am not convinced with my digital thermal reader so need to try another. I couldn't locate a Automatic Bypass valve either. I have also attached photos of the pump speeds at the time the temps were recorded. At the moment the system is working but this was the case when the temperatures were in double figures, the problem was when it dropped to 9deg and below.
When you have a reliable means of temperature measurement please repeat the test.
Obviously I cannot be 100% certain, but I suspect that your problem is due to the design of the system and the way it is being operated.
This is what I suspect is happening.
During milder weather conditions, the room thermostats will periodically operate some of the UFH solenoid valves, and run the corresponding water pump for that UFH manifold. This will draw warm water from the buffer tank at a rate dependent upon how many loops have operated and how many water pumps are running.
The main water pump will be feeding warm water from the heat pump into the buffer tank, at a rate greater than the flow coming out and going to the UFH loops.
As the outside air temperature (OAT) reduces, the heating demand will increase and more UFH loops will be activated, which in turn will increase the water flow rate from the buffer tank. I suspect that at an OAT of 9C and below, the flow rate being drawn by the three UFH water pumps becomes greater than the flow rate from the main water pump pushing water into the buffer tank. This would cause the temperature of the water being supplied to the UFH loops to reduce, rather than increase, because mixing is occurring within the buffer tank.
Before making any changes I would suggest repeating the temperature measurements during milder conditions and again when the OAT falls below 9C.
If my theory is proven to be correct then you could try the following. Reduce the speed of the three UFH manifold water pumps to their lowest setting and increase the speed of the main water pump to its highest setting.
I would also suggest that you check the specification of all the water pumps, since the main water pump is required to have a higher flow rate than the three UFH manifold pumps combined. If you are not certain how to check this then post close-up photo's of all the water pumps showing their model number.
Now that we have had a cold snap in the weather I recorded the relevant info as previously mentioned. The system has been good up until Friday where the outside temperature dropped and then it was unable to achieve the required flow temperatures.
So same old issue that for some reason its not able to get the flow temps in temperatures below 7deg, which baffles me as it has no issues to reach these for the hot water, if any
thing the flow temp is a lot higher for this so why cant it do this for the heating?
Now that we have had a cold snap in the weather I recorded the relevant info as previously mentioned. The system has been good up until Friday where the outside temperature dropped and then it was unable to achieve the required flow temperatures.
So same old issue that for some reason its not able to get the flow temps in temperatures below 7deg, which baffles me as it has no issues to reach these for the hot water, if any
thing the flow temp is a lot higher for this so why cant it do this for the heating?
If your heat pump is keeping your home warm at a lower LWT then that is a good thing, since it means that your heat pump is operating more efficiently.
@derek-m That's the issue is that it works when the OAT is above say 8deg and achieves the required flow temps to heat the house but once the OAT drops say 7deg and below it doesn't achieve the flow temps (drops to mid 30's) and resulting in the heat pump running for days on end with the stats calling for heat but the house doesn't heat as required. Surely the flow temps need to be maintained/reach the set flow temps of 45deg to provide the heat even though the OAT drops.
@derek-m That's the issue is that it works when the OAT is above say 8deg and achieves the required flow temps to heat the house but once the OAT drops say 7deg and below it doesn't achieve the flow temps (drops to mid 30's) and resulting in the heat pump running for days on end with the stats calling for heat but the house doesn't heat as required. Surely the flow temps need to be maintained/reach the set flow temps of 45deg to provide the heat even though the OAT drops.
Okay, time to go back to basics.
What is the size and type of your home? What is the heat loss calculation for your home? What is the output capacity of your heat pump? Has the system ever work correctly and if so what has been changed?
Is the controller operating in Fixed LWT mode, WC mode or AA mode?
@derek-m Home Size is 450sq/m traditional build with external/internal block walls with cavity and stone faced and some large glazing. The floors are bock and bean also. Heat Loss calcs I have attached the document along with the heat pump spec. Not sure what the terms are for the controller operation? From my understanding its set in weather compensation mode with the curve settings on +2
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